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Page No 99:
Question 1:
Akhila went to a fair in her village. She wanted to enjoy rides in the Giant Wheel and play Hoopla (a game in which you throw a rig on the items kept in the stall, and if the ring covers any object completely you get it.) The number of times she played Hoopla is half the number of rides she had on the Giant Wheel. Each ride costs Rs 3, and a game of Hoopla costs Rs 4. If she spent Rs 20 in the fair, represent this situation algebraically and graphically.
Answer:
Let no. of ride is and no. of Hoopla is .He paid Rs 20 for ride and for Hoopla.
The cost of ride is Rs and cost of Hoopla is Rs.then
The number of Hoopla is the half number of ride, then
Hence algebraic equations are and
Now, we draw the graph for algebraic equations.
Page No 99:
Question 2:
Aftab tells his daughter, "Seven years ago, I was seven times as old as you were then. Also, three years from now, I shall be three times as old as you will be". Is not this interesting? Represent this situation algebraically and graphically.
Answer:
Let age of Aftab is years and age of his daughter is years. Years ago his age wastimes older as her daughter was. Then
Three years from now, he will be three times older as his daughter will be, then
Hence the algebraic representation are and
Page No 99:
Question 3:
The path of a train A is given by the equation 3x + 4y − 12 = 0 and the path of another train B is given by the equation 6x + 8y − 48 = 0. Represent this situation graphically.
Answer:
The given equation are and.
In order to represent the above pair of linear equation graphically, we need
Two points on the line representing each equation. That is, we find two solutions
of each equation as given below:
We have,
Putting we get
Putting we get
Thus, two solution of equation are
We have
Putting we get
Putting we get
Thus, two solution of equation are
8 | ||
6 |
Now we plot the pointand and draw a line passing through
These two points to get the graph o the line represented by equation
We also plot the points and and draw a line passing through
These two points to get the graph O the line represented by equation
We observe that the line parallel and they do not intersect anywhere.
Page No 99:
Question 4:
Gloria is walking along the path joining (−2, 3) and (2, −2), while Suresh is walking along the path joining (0, 5) and (4, 0). Represent this situation graphically.
Answer:
Gloria is walking the path joining and
Suresh is walking the path joining and
0 | 4 | |
5 | 0 |
The graphical representations are
Page No 99:
Question 5:
On comparing the ratios , and without drawing them, find out whether the lines representing the following pairs of linear equations intersect at a point, are parallel or coincide :
(i) 5x − 4y + 8 = 0
7x + 6y − 9 = 0
(ii) 9x + 3y + 12 = 0
18x + 6y + 24 = 0
(iii) 6x − 3y + 10 = 0
2x − y + 9 = 0
Answer:
(i) Given equation are: 5x + 4y + 8 = 0
7x + 6y − 9 = 0
We have And
Thus the pair of linear equation is intersecting.
(ii) Given equation are: 9x + 3y + 12 = 0
18x + 6y + 24 = 0
We have
Thus the pair of linear is coincident lines.
(iii) Given equation are:
We have
Thus the pair of line is parallel lines.
Page No 99:
Question 6:
Given the linear equation 2x + 3y − 8 = 0, write another linear equation in two variables such that the geometrical representation of the pair so formed is :
(i) intersecting lines
(ii) parallel lines
(iii) coincident lines
Answer:
(i) Given the linear equation are:
We know that intersecting condition:
Where
Hence the equation of other line is
(ii) We know that parallel line condition is:
Where
Hence the equation is
(iii) We know that coincident line condition is:
Where
Hence the equation is
Page No 99:
Question 7:
The cost of 2kg of apples and 1 kg of grapes on a day was found to be Rs 160. After a month, the cost of 4 kg of apples and 2kg of grapes is Rs. 300 Represent th situation algebraically and geometrically.
Answer:
Let the cost of 1 kg of apples be Rs x.
And, cost of 1 kg of grapes = Rs y
According to the question, the algebraic representation is
For ,
The solution table is
x | 50 | 60 | 70 |
y | 60 | 40 | 20 |
For 4x + 2y = 300,
The solution table is
x | 70 | 80 | 75 |
y | 10 | –10 | 0 |
The graphical representation is as follows.
Page No 108:
Question 1:
Solve the following systems of equations graphically:
x – y + 1 = 0
3x + 2y – 12 = 0
Answer:
The given equations are:
x – y + 1 = 0 ...(i)
3x + 2y – 12 = 0 ...(ii)
Solving equation (i), we get
When x = 0, y = 1
When x = 1, y = 2
x | 0 | 1 |
y | 1 | 2 |
Solving equation (ii), we get
â
When x = 0, y = 6
When x = 4, y = 0
x | 0 | 4 |
y | 6 | 0 |
On plotting these points on a graph, we get
Hence, point A(2, 3) is the point of intersection.
Page No 108:
Question 2:
Solve the following systems of equations graphically:
2x − 3y + 13 = 0
3x − 2y + 12 = 0
Answer:
The given equations are:
Putting in equation we get:
Putting in equationwe get
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Graph of the equation….
Putting in equationwe get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
The two lines intersect at points P.
Hence, and is the solution.
Page No 108:
Question 3:
Show graphically that each one of the following systems of equations has infinitely many solutions:
2x + 3y = 6
4x + 6y = 12
Answer:
The given equations are
Putting in equation we get:
Putting in equation we get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Graph of the equation….
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Thus the graph of the two equations coincide
Consequently, every solution of one equation is a solution of the other.
Hence the equations have infinitely many solutions.
Page No 108:
Question 4:
Show graphically that each one of the following systems of equations has infinitely many solutions:
x − 2y + 11 = 0
3x − 6y + 33 = 0
Answer:
The given equations are
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Graph of the equation….
Putting in equation we get:
Putting in equationwe get
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Thus the graph of the two equations are coincide
Consequently, every solution of one equation is a solution of the other.
Hence the equations have infinitely many solutions.
Page No 108:
Question 5:
Show graphically that each one of the following systems of equations is in-consistent (i.e. has no solution) :
3x − 5y = 20
6x − 10y = −40
Answer:
The given equations are
Putting in equation we get:
Putting in equationwe get
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Graph of the equation….
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Here we see that the two lines are parallel
Hence the given system of equations has no solution.
Page No 108:
Question 6:
Show graphically that each one of the following systems of equations is in-consistent (i.e. has no solution) :
3x − 4y − 1 = 0
Answer:
The given equations are
Putting in equation we get:
Putting in equation we get:
Use the following table to draw the graph.
The graph of (i) can be obtained by plotting the two points.
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Here, the two lines are parallel.
Hence the given system of equations is inconsistent.
Page No 109:
Question 7:
Determine graphically the vertices of the triangle, the equations of whose sides are given below :
(i) 2y − x = 8, 5y − x = 14 and y − 2x = 1
(ii) y = x, y = 0 and 3x + 3y = 10
Answer:
(i) Draw the 3 lines as given by equations
By taking x=1 = 1 cm on x−axis
And y =1=1cm on y−axis
Clearly from graph points of intersection three lines are
(−4,2) , (1,3), (2,5)
(ii) Draw the 3 lines as given by equations
By taking x=1 = 1 cm on x−axis
And y =1=1cm on y−axis
From graph point of intersection are (0,0) (10/3,0) (5/3,5/3)
Page No 109:
Question 8:
Determine, graphically whether the system of equations x − 2y = 2, 4x − 2y = 5 is consistent or in-consistent.
Answer:
The given equations are
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
0 | 5/4 | |
–5/2 | 0 |
Draw the graph by plotting the two points from table.
It has unique solution.
Hence the system of equations is consistent
Page No 109:
Question 9:
Determine, by drawing graphs, whether the following system of linear equations has a unique solution or not :
(i) 2x − 3y = 6, x + y = 1
(ii) 2y = 4x − 6, 2x = y + 3
Answer:
(i) The given equations are
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Graph of the equation….
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
The two lines intersect at point .
Hence the equations have unique solution.
(ii) The equations of graphs is
Putting in equation we get:
Putting in equation we get:
Use the following table to draw the graph.
The graph of (i) can be obtained by plotting the two points .
Graph of the equation
Putting in equation we get.
Putting in equation we get.
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
The two lines are coincident.
Hence the equations have infinitely much solution.
Hence the system is consistent
Page No 109:
Question 10:
âSolve graphically each of the following systems of linear equations. Also find the coordinates of the points where the lines meet axis of y.
(i) 2x − 5y + 4 = 0, 2x + y − 8 = 0
(ii) 3x + 2y = 12, 5x − 2y = 4
Answer:
â(i) The given equations are
The two points satisfying (i) can be listed in a table as,
0 | 8 | |
4 |
The two points satisfying (ii) can be listed in a table as,
4 | 2 | 0 | |
0 | 4 | 8 |
Now, graph of equations (i) and (ii) can be drawn as,
It is seen that the solution of the given system of equations is given by x = 3, y = 2.
Also, it is observed that the lines (i) and (ii) meet the y-axis at the points respectively.
(ii) The given equations are
The two points satisfying (i) can be listed in a table as,
4 | 0 | |
0 | 6 |
The two points satisfying (ii) can be listed in a table as,
0 | 3 | |
−2 | 5.5 |
Now, graph of equations (i) and (ii) can be drawn as,
It is seen that the solution of the given system of equations is given by x = 2, y = 3.
Also, it is observed that the lines (i) and (ii) meet the y-axis at the points respectively.
Page No 109:
Question 11:
Solve the following system of linear equations graphically and shade the region between the two lines and x-axis:
â(i) 2x + 3y = 12, x − y = 1
(ii) 3x + 2y − 4 = 0, 2x − 3y − 7 = 0
Answer:
â(i) The given equations are:
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
The two lines intersect at. The region enclosed by the lines represented by the given equations and x-axis are shown in the above figure.
Hence, and is the solution.
(ii) The given equations are:
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
0 | ||
2 | 0 |
The graph of (i) can be obtained by plotting the two points .
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
− |
Draw the graph by plotting the two points from table.
The two lines intersect at. The area enclosed by the lines represented by the given equations and the coordinates x-axis and shaded the area in graph.
Hence, and is the solution.
Page No 109:
Question 12:
Draw the graphs of the following equations on the same graph paper.
2x + 3y = 12,
x − y = 1
Find the coordinates of the vertices of the triangle formed by the two straight lines and the y-axis.
Answer:
The given equations are
Putting in equation we get:
Putting in equation we get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Draw the graph by plotting the two points from table.
The intersection point is P(3, 2)
Three points of the triangle are.
Hence the value of and
Page No 109:
Question 13:
Draw the graphs of x − y + 1 = 0 and 3x + 2y − 12 = 0. Determine the coordinates of the vertices of the triangle formed by these lines and x-axis and shade the triangular area. Calculate the area bounded by these lines and x-axis.
Answer:
The given equations are
Putting in equation we get:
Putting in equation (i) we get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table.
The two lines intersect at.
Now, Required area = Area of shaded region
Required area = Area of PBD
Required area =
Required area =
Required area =
Hence the area =
Page No 109:
Question 14:
Draw the graphs of the equations 5x − y = 5 and 3x − y = 3. Determine the co-ordinates of the vertices of the triangle formed by these lines and y-axis. Calculate the area of the triangle so formed.
Answer:
The given equations are:
Putting in equation (i) we get:
Putting in equation (i) we get:
Use the following table to draw the graph.
Draw the graph by plotting the two points from table
Putting in equation we get:
Putting in equationwe get:
Use the following table to draw the graph.
–3 |
Draw the graph by plotting the two points from table.
Hence the vertices of the required triangle are.
Now,
Required area = Area of PCA
Required area =
Required area =
Hence the required area is
Page No 109:
Question 15:
âForm the pair of linear equations in the following problems, and find their solution graphically:
(i) 10 students of class X took part in Mathematics quiz. If the number of girls is 4 more than the number of boys, find the number of boys and girls who took part in the quiz.
(ii) 5 pencils and 7 pens together cost â¹ 50, whereas 7 pencils and 5 pens together cost â¹ 46. Find the cost of one pencil and a pen.
Answer:
â(i) Let the number of girls be x and the number of boys be y.
According to the question, the algebraic representation is
x + y = 10
x − y = 4
For x + y = 10,
x = 10 − y
x | 5 | 4 | 6 |
y | 5 | 6 | 4 |
For x − y = 4,
x = 4 + y
x | 5 | 4 | 3 |
y | 1 | 0 | −1 |
Hence, the graphic representation is as follows.
From the figure, it can be observed that these lines intersect each other at point (7, 3).
Therefore, the number of girls and boys in the class are 7 and 3 respectively.
(ii) Let the cost of 1 pencil be â¹ x and the cost of 1 pen be â¹ y.
According to the question, the algebraic representation is
5x + 7y = 50
7x + 5y = 46
For 5x + 7y = 50,
x | 3 | 10 | − 4 |
y | 5 | 0 | 10 |
7x + 5y = 46
x | 8 | 3 | − 2 |
y | − 2 | 5 | 12 |
Hence, the graphic representation is as follows.
From the figure, it can be observed that these lines intersect each other at point (3, 5).
Therefore, the cost of a pencil and a pen are â¹ 3 and â¹ 5 respectively.
Page No 109:
Question 16:
Draw the graphs of the following equations:
2x − 3y + 6 = 0
2x + 3y − 18 = 0
y − 2 = 0
Find the vertices of the triangle so obtained. Also, find the area of the triangle.
Answer:
The given equations are
The two points satisfying (i) can be listed in a table as,
−3 | 6 | |
0 | 6 |
The two points satisfying (ii) can be listed in a table as,
0 | 9 | |
6 | 0 |
The two points satisfying (iii) can be listed in a table as,
−1 | 8 | |
2 | 2 |
Now, graph of equations (i), (ii) and (iii) can be drawn as,
It is seen that the coordinates of the vertices of the obtained triangle are
∴Area of ΔABC =
Page No 109:
Question 17:
Champa went to a 'sale' to purchase some pants and skirts. When her friends asked her how many of each she had bought, she answered, "The number of skirts is two less than twice the number of pants purchased. Also the number of skirts is four less than four times the number of pants purchased." Help her friends to find how many pants and skirts Champa bought.
Answer:
âLet us denote the number of pants by x and the number of skirts by y. Then the equations formed are :
y = 2x − 2 … (i)
y = 4x − 4 … (ii)
The graphs of the equations (i) and (ii) can be drawn by finding two solutions for each of the equations. They are given in the following table.
x | 2 | 0 |
y = 2x − 2 | 2 | −2 |
y = 4x − 4 | 4 | −4 |
Hence, the graphic representation is as follows.
The two lines intersect at the point (1, 0).
So, x = 1, y = 0 is the required solution of the pair of linear equations, i.e., the number of pants she purchased is 1 and she did not buy any skirt.
Page No 110:
Question 18:
Given the linear equation 2x + 3y − 8 = 0, write another linear equation in two variables such that the geometrical representation of the pair so formed is
(i) intersecting lines
(ii) Parallel lines
(iii) coincident lines
Answer:
(i) For intersecting lines,
Equation of another intersecting line to the given line is−
Since, condition for intersecting lines and unique solution is−
(ii) For parallel lines,
Equation of another parallel line to the given line is−
Since, condition for parallel lines and no solution is−
(iii) For co−incident lines,
Equation of another coincident line to the given line is−
Since, condition for coincident lines and infinite solution is−
Page No 110:
Question 19:
Graphically , solve the following pair of equations:
Find the ratio of the areas of the two triangles formed by the lines representing these equations with the x-axis and the lines with the y-axis.
Answer:
The given linear equations are:
For (i), we have
x | 0 | 3 |
y | 6 | 0 |
For (ii), we have
x | 0 | −1 |
y | 2 | 0 |
Thus, we plot the graph for these two equations and mark the point where these two lines intersect.
From the graph we see that the two lines intersect at point E(1, 4).
Now, the area of triangle CEB is
The area of triangle AED is
So, the ratio of the areas of the two triangles will be
Thus, the required ratio is 4 : 1.
Page No 110:
Question 20:
Determine, graphically, the vertices of the triangle formed by the lines
Answer:
The given lines are:
From (i), we have
x | 1 | 2 |
y | 1 | 2 |
For (ii), we have
x | 0 | 3 |
y | 0 | 1 |
For (iii), we have
x | 0 | 8 |
y | 8 | 0 |
Thus, we plot the graph for these three equations and mark the point where these two lines intersect.
From the graph we find that the vertices of the triangle thus formed are H(4, 4), I(6, 2) and D(0, 0).
Page No 110:
Question 21:
Draw the graph of the equations x = 3 , x = 5 and 2x − y − 4 = 0 . Also, find the area of the quadrilateral formed by the lines and the x-axis.
Answer:
The given equations are
x = 3 .....(i)
x = 5 .....(ii)
2x − y − 4 = 0 .....(iii)
For (iii), we have
x | 0 | 2 |
y | −4 | 0 |
We plot the lines on the graph as follows:
The vertices of the quadrilateral thus formed are A(5, 0), B(5, 6), C(3, 2) and D(3, 0).
∴ Area of the quadrilateral DABC
= Area of a trapezium
=
Thus, the area of the quadrilateral formed by the given lines and the x-axis is 8 square units.
Page No 110:
Question 22:
Draw the graph of the lines x = 2 and y = 3 . Write the vertices of the figure formed by these lines , the x-axis and the y-axis . Also , find the area of the figure.
Answer:
The given lines are
The graph thus obtained will be as follows:
The figure thus obtained is a rectangle ABCD. The vertices of the rectangle are A(−2, 3), B(0, 3), C(0, 0) and D(−2, 0).
Length of the rectangle = AD = BC = 3 units
Breadth of the rectangle = CD = AB = 2 units
∴ Area of rectangle ABCD
Page No 118:
Question 1:
Find the values of x and y in the following rectangle.
Answer:
ABCD is the given rectangle. So, AB = CD and AD = BC.
Thus,
Adding (i) and (ii), we get
4x + 4y = 20
Subtracting (i) from (ii), we get
2x − 2y = −6
Adding (iii) and (iv), we get
2x = 2
Putting x = 1 in (iii), we get
1 + y = 5
⇒ y = 4
Thus, x = 1 and y = 4.
Page No 118:
Question 2:
Solve the following systems of equations:
Answer:
The given equations are:
Multiply equation by 2 and equation by 15, and add both equations we get
Put the value of in equationwe get
Hence the value of and
Page No 118:
Question 3:
Solve the following systems of equations:
Answer:
The given equations are:
…
Subtract (ii) from (i) we get
Put the value of in equation we get
Hence the value of and .
Page No 118:
Question 4:
Solve the following systems of equations:
Answer:
The given equations are:
…
…
Multiply equation by and equation by and add both equations we get
Put the value of in equation we get
Hence the value of and .
Page No 118:
Question 5:
Solve the following systems of equations:
Answer:
The given equations are:
…
…
Multiply equation by and equation by and add both equations we get
Put the value of in equation we get
Hence the value of and .
Page No 118:
Question 6:
Solve the following systems of equations:
Answer:
The given equations are:
Multiply equation (1) by , we get
adding (2) and (3), we getHence the value of x and y are and
Page No 118:
Question 7:
Solve the following systems of equations:
Answer:
The given equations are:
…
…
Multiply equation by and equation by, add both equations, we get
Put the value of in equation, we get
Hence the value of and .
Page No 118:
Question 8:
Solve the following systems of equations:
Answer:
The given equations are:
…
…
Multiply equation by and equation by 3 and add both equations we get
Put the value of in equation, we get
Hence the value of and .
Page No 118:
Question 9:
Solve the following systems of equations:
Answer:
The given equations are:
…
…
Multiply equation by and add both equations we get
Put the value of in equation, we get
Hence the value of and
Page No 118:
Question 10:
Solve the following systems of equations:
0.5x + 0.7y = 0.74
0.3x + 0.5y = 0.5
Answer:
The given equations are:
…
…
Multiply equation by and by and subtract equation (ii) from (i) we get
Put the value of in equation, we get
Hence the value of and
Page No 118:
Question 11:
Solve the following systems of equations:
Answer:
The given equations are:
…
…
Multiply equation by and equation by and subtract equation (ii) from (i), we get
Put the value of in equation, we get
Hence the value of and
Page No 118:
Question 12:
Solve the following systems of equations:
where x + y ≠ 0, y − x ≠ 0
Answer:
The given equations are:
Add both equations, we get
Put the value of in equation, we get
Hence the value of and
Page No 118:
Question 13:
Solve the following systems of equations:
x ≠ 0, y ≠ 0
Answer:
The given equations are:
…
…
Add both equations we get
Put the value of in equation, we get
Hence the value of and .
Page No 118:
Question 14:
Solve the following systems of equations:
Answer:
The given equations are:
Let and then equations are
…
…
Multiply equation by and equation by add both equations, we get
Put the value of in equation, we get
Then
…
…
Add both equations, we get
Put the value of in equation we get
Hence the value of and
Page No 118:
Question 15:
Solve the following systems of equations:
Answer:
The given equations are:
Let and then equations are
…
…
Multiply equation by and add both equations, we get
Put the value of in equation, we get
Then
Hence the value of and .
Page No 119:
Question 16:
Solve the following systems of equations:
Answer:
The given equations are:
Let and then equations are
…
…
Multiply equation by and equation by and add both equations, we get
Put the value of in equation, we get
Then
Add both equations, we get
Put the value of in equation we get
Hence the value of and .
Page No 119:
Question 17:
Solve the following systems of equations:
Answer:
The given equations are:
Let and then equations are
…
…
Multiply equation by and add both equations, we get
Put the value of in equation, we get
Then
…
…
Add both equations, we get
Put the value of in equation we get
Hence the value of and
Page No 119:
Question 18:
Solve the following systems of equations:
Answer:
The given equations are:
…
…
Multiply equation by and equation by, add both equations we get
Put the value of in equation, we get
Hence the value of and
Page No 119:
Question 19:
Solve the following systems of equations:
152x − 378y = −74
−378x + 152y = −604
Answer:
The given equations are:
…
…
Multiply equation by and equation by and add both equations we get
Put the value of in equation, we get
Hence the value of and
Page No 119:
Question 20:
Solve the following systems of equations:
99x + 101y = 499
101x + 99y = 501
Answer:
The given equations are:
…
…
Multiply equation by and equation by, and subtract (ii) from (i) we get
Put the value of in equation, we get
Hence the value of and
Page No 119:
Question 21:
21x + 47y = 110
47x + 21y = 162
Answer:
21x + 47y = 110 .....(i)
47x + 21y = 162 .....(ii)
Adding(i) and (ii), we get
68x + 68y = 272
.....(iii)
Subtracting (i) from (ii), we get
Adding (iii) and (iv), we get
Putting x = 3 in (iv), we get
3 − y = 2
⇒ y = 1
Page No 119:
Question 22:
If (x + 1) is a factor of , then find the values of a and b given that 2a − 3b = 4.
Answer:
Since (x + 1) is a factor of , so
Also, we are given
2a − 3b = 4 .....(ii)
From (i) and (ii) we get
Putting b = 2 in (iii), we get
a = 1 + 2 × 2 = 5
Thus, the value of a = 5 and b = 2.
Page No 119:
Question 23:
Find the solution of the pair of equations and . Hence , find , if .
Answer:
The given equations are
Multiplying (i) by 2, we get
Subtracting (ii) from (iii), we get
x = 340
Putting x = 340 in (i), we get
340 + 2y = 10
⇒ 2y = 10 − 340 = −330
⇒ y = −165
Now, in order to find the value of , we simply put the value of x and y in the equation .
Thus, the value of .
Page No 119:
Question 24:
Write an equation of a line passing through the point representing solution of the pair of linear equations . How many such lines can we find ?
Answer:
The given equations are
Adding (i) and (ii), we get
3x = 3
⇒ x = 1
Putting x = 1 in (i), we get
1 + y = 2
⇒ y = 1
Thus, the solution of the given equations is (1, 1).
We know that, infinitely many straight lines pass through a single point.
So, the equation of one such line can be 3x + 2y = 5 or 2x + 3y = 5.
Page No 119:
Question 25:
Write a pair of linear equations which has the unique solution How many such pairs can you write ?
Answer:
The unique solution is given as x = −1 and y = 3.
The one pair of linear equations having x = −1 and y = 3 as unique solution can be
12x + 5y = 3
2x + y = 1
Similarly, infinitely many pairs of linear equations are possible.
Page No 127:
Question 1:
Solve each of the following systems of equations by the method of cross-multiplication :
3x + 2y + 25 = 0
2x + y + 10 = 0
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
By cross multiplication method we get
Also
Hence we get the value of and
Page No 127:
Question 2:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
Let
By cross multiplication method we get
So
We know that
Hence we get the value of and
Page No 127:
Question 3:
Solve each of the following systems of equations by the method of cross-multiplication :
ax + by = a − b
bx − ay = a + b
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
T
Thereforeand
Hence we get the value of and
Page No 127:
Question 4:
Solve each of the following systems of equations by the method of cross-multiplication :
ax + by = a2
bx + ay = b2
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
And
Hence we get the value of and
Page No 127:
Question 5:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
Now rewriting the given equation as
By cross multiplication method we get
Consider the following for u
Consider the following for v
We know that
Now adding eq. (3) and (4) we get
And after substituting the value of x in eq. (4) we get
Hence we get the value of and
Page No 127:
Question 6:
Solve each of the following systems of equations by the method of cross-multiplication :
5ax + 6by = 28
3ax + 4by = 18
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
Consider the following to calculate x
And
Hence we get the value of and
Page No 127:
Question 7:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
Now for y
Hence we get the value of and
Page No 127:
Question 8:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
Hence we get the value of
Page No 127:
Question 9:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
For y
Hence we get the value of and
Page No 127:
Question 10:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
And
Hence we get the value of and
Page No 127:
Question 11:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
And
Hence we get the value ofand
Page No 127:
Question 12:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
Let
Rewriting equations
Now, by cross multiplication method we get
For u consider the following
For y consider
We know that
Now
Hence we get the value of and
Page No 127:
Question 13:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
And
Hence we get the value of and
Page No 127:
Question 14:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
After rewriting equations
By cross multiplication method we get
For y consider the following
Hence we get the value of and
Page No 127:
Question 15:
Solve each of the following systems of equations by the method of cross-multiplication :
(a + 2b)x + (2a − b)y = 2
(a − 2b)x + (2a + b)y = 3
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
And
Hence we get the value of and
Page No 127:
Question 16:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
Consider the following for x
Now consider the following for y
Hence we get the value of and
Page No 127:
Question 17:
Solve each of the following systems of equations by the method of cross-multiplication :
Answer:
GIVEN:
To find: The solution of the systems of equation by the method of cross-multiplication:
Here we have the pair of simultaneous equation
By cross multiplication method we get
Consider the following for x
Now for y
Hence we get the value of and
Page No 137:
Question 1:
In each of the following systems of equations determine whether the system has a unique solution, no solution or infinitely many solutions. In case there is a unique solution, find it:
x − 3y = 3
3x − 9y = 2
Answer:
GIVEN:
To find: To determine whether the system has a unique solution, no solution or infinitely many solutions
We know that the system of equations
For unique solution
For no solution
For infinitely many solution
Here,
Since which means hence the system of equation has no solution.
Hence the system of equation has no solution
Page No 137:
Question 2:
In each of the following systems of equations determine whether the system has a unique solution, no solution or infinitely many solutions. In case there is a unique solution, find it
2x + y = 5
4x + 2y = 10
Answer:
GIVEN:
To find: To determine whether the system has a unique solution, no solution or infinitely many solutions
We know that the system of equations
For unique solution
For no solution
For infinitely many solution
Here,
Since which means hence the system of equation has infinitely many solution.
Hence the system of equation has infinitely many solutions
Page No 137:
Question 3:
Find the value of k for which the following system of equations has a unique solution:
kx + 2y = 5
3x + y = 1
Answer:
GIVEN:
To find: To determine to value of k for which the system has a unique solution.
We know that the system of equations
For unique solution
Here,
Hence for the system of equation has unique solution.
Page No 137:
Question 4:
Find the value of k for which the following system of equations has a unique solution:
Answer:
GIVEN:
To find: To determine to value of k for which the system has a unique solution.
We know that the system of equations
For unique solution
Here,
Hence for the system of equation has unique solution
Page No 137:
Question 5:
Find the value of k for which each of the following system of equations have infinitely many solutions :
Answer:
GIVEN:
To find: To determine for what value of k the system of equation has infinitely many solutions
We know that the system of equations
For infinitely many solution
Here,
Consider the following for k
Now consider the following
Hence for the system of equation have infinitely many solutions.
Page No 137:
Question 6:
Find the value of k for which each of the following system of equations have infinitely many solutions :
Answer:
GIVEN:
To find: To determine for what value of k the system of equation has infinitely many solutions
We know that the system of equations
For infinitely many solution
Here,
Hence for the system of equation have infinitely many solutions.
Page No 137:
Question 7:
Find the value of k for which each of the following system of equations have infinitely many solutions :
Answer:
GIVEN:
To find: To determine for what value of k the system of equation has infinitely many solutions
We know that the system of equations
For infinitely many solution
Here,
Consider the following relation to find k
Now again consider the following
Hence for the system of equation have infinitely many solutions
Page No 137:
Question 8:
Find the value of k for which each of the following system of equations have infinitely many solutions :
Answer:
GIVEN:
To find: To determine for what value of k the system of equation has infinitely many solutions
We know that the system of equations
For infinitely many solution
Here
Now again consider the following to find k
Hence for the system of equation have infinitely many solutions
Page No 137:
Question 9:
Find the value of k for which each of the following system of equations have no solution :
2x + ky = 11
5x − 7y = 5
Answer:
GIVEN:
To find: To determine for what value of k the system of equation has no solution
We know that the system of equations
For no solution
Here,
Hence for the system of equation has no solution.
Page No 137:
Question 10:
Find the value of k for which each of the following system of equations have no solution :
cx + 2y = 3
12x + cy = 6
Answer:
GIVEN:
To find: To determine for what value of c the system of equation has no solution
We know that the system of equations
For no solution
Here,
Hence for the system of equation has no solution.
Page No 138:
Question 11:
Find the value of k for which the following system of equations has no solution:
kx + 3y = k − 3
12x + ky = k
Answer:
âkx + 3y = k − 3
12x + ky = k
We know that the system of equations
Has no solution when,
Here,
Consider the following for k
Now consider the following
Thus, the common value of k is −6.
Hence for k = −6 the system of equation has no solution.
Page No 138:
Question 12:
âFind c if the system of equations cx + 3y + 3 – c = 0, 12x + cy – c = 0 has infinitely many solutions?
Answer:
If the system of equations has infinitely many solutions, then .
Since, the system of equations cx + 3y + 3 – c = 0, 12x + cy – c = 0 has infinitely many solutions
Therefore,
Hence, the value of c is 6.
Page No 138:
Question 13:
Find the values of k for which the system will have (i) a unique solution, and (ii) no solution. Is there a value of k for which the system has infinitely many solutions?
2x + ky = 1
3x − 5y = 7
Answer:
GIVEN:
To find: To determine for what value of k the system of equation has
(1) Unique solution
(2) No solution
(3) Infinitely many solution
We know that the system of equations
(1) For Unique solution
Here,
Hence for the system of equation has unique solution
(2) For no solution
Here,
Hence for the system of equation has no solution
(3) For infinitely many solution
Here,
But since here
Hence the system does not have infinitely many solutions.
Page No 138:
Question 14:
For what value of k, the following system of equations will represent the coincident lines?
x + 2y + 7 = 0
2x + ky + 14 = 0
Answer:
GIVEN:
To find: To determine for what value of k the system of equation will represents coincident lines
We know that the system of equations
For the system of equation to represent coincident lines we have the following relation
Here,
Hence for the system of equation represents coincident lines
Page No 138:
Question 15:
Determine the values of a and b so that the following system of linear equations have infinitely many solutions :
(2a − 1) x + 3y − 5 = 0
3x + (b − 1)y − 2 = 0
Answer:
GIVEN:
To find: To determine for what value of k the system of equation has infinitely many solutions
We know that the system of equations
For infinitely many solution
Here
Again consider
Hence for and the system of equation has infinitely many solution.
Page No 138:
Question 16:
For which value(s) of , do the pair of linear equations and have
(i) no solution ? (ii) infinitely many solutions ?
(iii) a unique solution ?
Answer:
The given linear equations are
(i) We know that the system of equations
will have no solution if
So,
Also,
Thus, the given system of equations has no solutions when .
(ii) We know that the system of equations
will have infinitely many solutions if
Also,
Thus, the given system of equations has infinitely many solutions when .
(iii) We know that the system of equations
will have a unique solution if
Thus, the given system of equations has a unique solution for all real values of except .
Page No 138:
Question 17:
Find the values of a and b for which the following system of equations has infinitely many solutions:
(i) (2a – 1)x – 3y = 5
(iii) 2x + 3y = 7
(iv) 2x + 3y – 7 = 0
(v) x + 2y = 1
(vi) 2x + 3y = 7
Answer:
âWe know that the system of equations
For infinitely many solution
(i) (2a – 1)x – 3y = 5
3x + (b – 2) y = 3
Here,
Hence for a = 3 and b = the system of equation has infinitely many solution.
Here
Consider the following
5a − 4b + 21 = 0……(1)
Again
a + b + 6 = 0…… (2)
Multiplying eq. (2) by 4 and adding eq. (1)
Putting the value of a in eq. (2)
Hence for and the system of equation has infinitely many solution.
(iii)
Here
Consider the following
…… (1)
Again consider the following
…… (2)
Multiplying eq. (2) by 2 and subtracting eq. (1) from eq. (2)
Substituting the value of b in eq. (2) we get
Hence forand the system of equation has infinitely many solution.
(iv)
Here
Consider the following
Hence, for a = 5 the system of equation have infinitely many solutions.
(v)
So,
Solving these two equations, we get
Putting b = 1 in a + b = 4, we get
a = 3
(vi)
Now,
⇒ a + b = 3a
⇒ b = 2a .....(1)
Also,
⇒ a + b = 12 .....(2)
Solving (1) and (2), we get
a = 4 and b = 8
Page No 140:
Question 1:
7 audio cassettes and 3 video cassettes cost Rs 1110, while 5 audio cassettes and 4 video cassettes cost Rs 1350. Find the cost of an audio cassette and a video cassette.
Answer:
Given:
(i) 7 Audio cassettes and 3 Video cassettes cost is 1110.
(ii) 5 Audio cassettes and 4 Video cassettes cost Rs. 1350.
To Find: Cost of 1 audio cassette and 1 video cassettes.
Let (i) the cost of 1 audio cassette = Rs. x.
(ii) the cost of 1 video cassette = Rs. y.
According to the given conditions, we have
Thus, we get the following system of linear equation,
By using cross multiplication, we have
Hence cost of 1 audio cassette =
Hence cost of 1 video cassette =
Page No 140:
Question 2:
Reena has pend and pencils which together are 40 in number. If she has 5 more pencils and 5 less pens, the number of pencils would become 4 times the number of pens. Find the original number of pens and pencils.
Answer:
Given:
(i) Total numbers of pens and pencils = 40.
(ii) If she has 5 more pencil and 5 less pens, the number of pencils would be 4 times the number of pen.
To find: Original number of pens and pencils.
Suppose original number of pencil = x
And original number of pen = y
According the given conditions, we have,
Thus we got the following system of linear equations
Substituting the value of y from equation 1 in equation 2 we get
Substituting the value of y in equation 1 we get
Hence we got the result number of pencils is and number of pens are
Page No 140:
Question 3:
The coach of a cricket team buys 7 bats and 6 balls for Rs 3800. Later, he buys 3 bats and 5 balls for Rs 1750. Find the cost of each bat and each ball.
Answer:
Given: (i) 7 bats and 6balls cost is Rs3800
(ii) 3 bats and 5balls cost is Rs1750
To find: Cost of 1 bat and 1 ball
Let (i) the cost of 1 bat = Rs. x.
(ii) the cost of 1 ball = Rs. y.
According to the given conditions, we have
Thus, we get the following system of linear equation,
7x + 6y − 3800 = 0 …… (1)
3x + 5y − 1750 = 0 …… (2)
By using cross multiplication, we have
Hence cost of 1 bat =
Hence cost of 1 ball =
Page No 140:
Question 4:
A lending library has a fixed charge for the first three days and additional charge for each day thereafter. Saritha paid Rs 27 for a book kept for seven days, while Susy paid Rs 21 for the book she kept for five days. Find the fixed charge and the charge for each extra day.
Answer:
To find:
(1) the fixed charge
(2) The charge for each day
Let the fixed charge be Rs x
And the extra charge per day be Rs y.
According to the given conditions,
Subtracting equation 1 and 2 we get
Substituting the value of y in equation 1 we get
Hence the fixed charge is and the charge of each day
Page No 141:
Question 5:
Jamila sold a table and a chair for â¹ 1050 , thereby making a profit of 10% on the table and 25% on the chair. If she had taken a profit of 25% on the table and 10% on the chair she would have got â¹ 1065. Find the cost price of each .
Answer:
Let the CP of the table be Rs x and that of the chair be Rs y.
Case I: Profit on table =
We know SP − CP = Profit
⇒ SP = Profit + CP
⇒ SP = + x =
Profit on chair =
SP = + y =
Total SP =
110x + 125y = 105000 .....(i)
Case II: Profit on table =
⇒ SP = Profit + CP
⇒ SP = + x =
Profit on chair =
SP = + y =
Total SP = + = 1065
125x + 110y = 106500 .....(ii)
From (i) and (ii), we have
235(x + y) = 211500
⇒ x + y = 900 .....(iii)
Subtracting (i) from (ii), we have
15(x − y) = 1500
⇒ x − y = 100 .....(iv)
Solving (iii) and (iv), we get
x = 500 and y = 400
Thus, CP of table = Rs 500 and CP of chair = Rs 400.
Page No 141:
Question 6:
Susan invested certain amount of money in two schemes A and B , which offer interest at the rate of 8% per annum and 9% per annum , respectively . She received â¹1860 as annual interest .However, had she interchanged the amount of investment in the two schemes , she would have received â¹20 more as annual interest . How much money did she invest in each scheme ?
Answer:
Let the money invested in Scheme A be Rs x and that in Scheme B be Rs y.
So, Interest in scheme A =
Interest in scheme B =
Total annual interest = + = 1860
⇒ 8x + 9y = 186000 .....(i)
After interchaning the amounts in the two schemes, the new total annual interest = .
Now,
= 1860 + 20 = 1880
⇒ 9x + 8y = 188000 .....(ii)
Adding (i) and (ii), we get
17x + 17y = 374000
⇒ x + y = 22000 .....(iii)
Subtracting (i) from (ii), we get
x − y = 2000 .....(iv)
Adding (iii) and (iv), we get
2x = 24000
⇒ x = 12000
Puting x = 12000 in (iii), we get
12000 + y = 22000
⇒ y = 10000
So, the money invested in scheme A = Rs 12,000 and in scheme B = Rs 10,000.
Page No 141:
Question 7:
The cost of 4 pens and 4 pencil boxes is â¹100 . Three times the cost of a pen is â¹15 more than the cost of a pencil box . Form the pair of linear equations for the above situation . Find the cost of a pen and a pencil box.
Answer:
Let the cost of 1 pen be â¹x and that of 1 pencil box be â¹y.
Now,
Cost of 4 pens + Cost of 4 pencil boxes = â¹100 (Given)
⇒ 4x + 4y = 100
⇒ x + y = 25 .....(i)
Also,
3 × Cost of a pen = Cost of a pencil box + â¹15
3x = y + 15
⇒ 3x − y = 15 .....(ii)
Adding (i) and (ii), we get
4x = 40
⇒ x = 10
Putting x = 10 in (i), we get
10 + y = 25
⇒ y = 15
Thus, the cost of a pen = â¹10 and that of a pencil box = â¹15.
Page No 141:
Question 8:
Vijay had some bananas , and he divided them into two lots A and B . He sold first lot at the rate of â¹2 for 3 bananas and the second lot at the rate of â¹1 per banana and got a total of â¹400 . If he had sold the first lot at the rate of â¹1 per banana and the second lot at the rate of â¹4 per five bananas, his total collection would have been â¹460 . Find the total number of bananas he had .
Answer:
Let the bananas in lot A be x and that in lot B be y.
Vijay sold 3 bananas for Rs 2 in lot A.
So, the cost of x bananas in lot A =
Now,
Cost of x bananas in lot A + Cost of y bananas in lot B = â¹400
⇒ 2x + 3y = 1200 .....(i)
Now, if he sells the first lot at the rate of Rs 1 per banana and second for Rs 4 for 5 bananas, then
= â¹460
⇒ 5x + 4y = 2300 .....(ii)
Solving (i) and (ii), we get
x = 300 and y = 200
So, the total number of bananas = x + y = 300 + 200 = 500.
Page No 141:
Question 9:
One says, "Give me a hundred, friend! I shall then become twice as rich as you." The other replies, "If you give me ten, I shall be six times as rich as you." Tell me what is the amount of their respective capital?
Answer:
To find:
(1) Total amount of A.
(2) Total amount of B.
Suppose A has Rs x and B has Rs y
According to the given conditions,
x + 100 = 2(y − 100)
x + 100 = 2y − 200
x − 2y = −300 ....(1)
and
y + 10 = 6(x − 10)
y + 10 = 6x − 60
6x − y = 70 ....(2)
Multiplying equation (2) by 2 we get
12x − 2y = 140 ....(3)
Subtracting (1) from (3), we get
11x = 440
x = 40
Substituting the value of x in equation (1), we get
40 − 2y = −300
−2y = −340
y = 170
Hence A has and B has
Page No 141:
Question 10:
A and B each have a certain number of mangoes. A says to B, "if you give 30 of your mangoes, I will have twice as many as left with you." B replies, "if you give me 10, I will have thrice as many as left with you." How many mangoes does each have?
Answer:
To find:
(1) Total mangoes of A.
(2) Total mangoes of B.
Suppose A has x mangoes and B has y mangoes,
According to the given conditions,
3x + 6y + 270 = 0 …… (3) and
Now adding eq.2 and eq.3
5y = 310
y =
Hence A has 34 mangoes and B has 62 mangoes.
Page No 145:
Question 1:
A number consist of two digits whose sum is five. When the digits are reversed, the number becomes greater by nine. Find the number.
Answer:
Let the digits at units and tens place of the given number be x and y respectively. Thus, the number is.
The sum of the digits of the number is 5. Thus, we have
After interchanging the digits, the number becomes.
The number obtained by interchanging the digits is greater by 9 from the original number. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
Adding the two equations, we have
Substituting the value of x in the first equation, we have
Hence, the number is.
Page No 145:
Question 2:
The sum of digits of a two number is 15. The number obtained by reversing the order of digits of the given number exceeds the given number by 9. Find the given number.
Answer:
Let the digits at units and tens place of the given number be x and y respectively. Thus, the number is.
The sum of the digits of the number is 15. Thus, we have
After interchanging the digits, the number becomes.
The number obtained by interchanging the digits is exceeding by 9 from the original number. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
Adding the two equations, we have
Substituting the value of x in the first equation, we have
Hence, the number is.
Page No 145:
Question 3:
The sum of two numbers is 1000 and the difference between their squares is 256000. Find the numbers.
Answer:
Let the numbers are x and y. One of them must be greater than or equal to the other. Let us assume that x is greater than or equal to y.
The sum of the two numbers is 1000. Thus, we have
The difference between the squares of the two numbers is 256000. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
Adding the two equations, we have
Substituting the value of x in the first equation, we have
Hence, the numbers are 628 and 372.
Page No 145:
Question 4:
A two-digit number is 4 times the sum of its digits. If 18 is added to the number, the digits are reversed. Find the number.
Answer:
Let the digits at units and tens place of the given number be x and y respectively. Thus, the number is.
The number is 4 times the sum of the two digits. Thus, we have
After interchanging the digits, the number becomes.
If 18 is added to the number, the digits are reversed. Thus, we have
So, we have the systems of equations
Here x and y are unknowns. We have to solve the above systems of equations for x and y.
Subtracting the first equation from the second, we have
Substituting the value of y in the first equation, we have
Hence, the number is.
Page No 145:
Question 5:
The sum of a two-digit number and the number formed by reversing the order of digit is 66. If the two digits differ by 2, find the number. How many such numbers are there?
Answer:
Let the digits at units and tens place of the given number be x and y respectively. Thus, the number is.
The two digits of the number are differing by 2. Thus, we have
After interchanging the digits, the number becomes.
The sum of the numbers obtained by interchanging the digits and the original number is 66. Thus, we have
So, we have two systems of simultaneous equations
Here x and y are unknowns. We have to solve the above systems of equations for x and y.
(i) First, we solve the system
Adding the two equations, we have
Substituting the value of x in the first equation, we have
Hence, the number is.
(ii) Now, we solve the system
Adding the two equations, we have
Substituting the value of x in the first equation, we have
Hence, the number is.
There are two such numbers.
Page No 145:
Question 6:
A two-digit number is 4 times the sum of its digits and twice the product of the digits. Find the number.
Answer:
Let the digits at units and tens place of the given number be x and y respectively. Thus, the number is.
The number is 4 times the sum of the two digits. Thus, we have
After interchanging the digits, the number becomes.
The number is twice the product of the digits. Thus, we have
So, we have the systems of equations
Here x and y are unknowns. We have to solve the above systems of equations for x and y.
Substituting in the second equation, we get
Or
Substituting the value of y in the first equation, we have
Hence, the number is.
Note that the first pair of solution does not give a two digit number.
Page No 145:
Question 7:
A two-digit number is such that the product of its digits is 20. If 9 is added to the number, the digits interchange their places. Find the number.
Answer:
Let the digits at units and tens place of the given number be x and y respectively. Thus, the number is.
The product of the two digits of the number is 20. Thus, we have
After interchanging the digits, the number becomes.
If 9 is added to the number, the digits interchange their places. Thus, we have
So, we have the systems of equations
Here x and y are unknowns. We have to solve the above systems of equations for x and y.
Substituting from the second equation to the first equation, we get
Or
Substituting the value of y in the second equation, we have
Hence, the number is.
Note that in the first pair of solution the values of x and y are both negative. But, the digits of the number can’t be negative. So, we must remove this pair.
Page No 145:
Question 8:
The sum of the digits of a two-digit number is 9. Also, nine times this number is twice the number obtained by reversing the order of the digits. Find the number.
Answer:
Let the digits at units and tens place of the given number be x and y respectively. Thus, the number is.
The sum of the two digits of the number is 9. Thus, we have
After interchanging the digits, the number becomes.
Also, 9 times the number is equal to twice the number obtained by reversing the order of the digits. Thus, we have
So, we have the systems of equations
Here x and y are unknowns. We have to solve the above systems of equations for x and y.
Substituting from the second equation to the first equation, we get
Substituting the value of y in the second equation, we have
Hence, the number is.
Page No 145:
Question 9:
Two numbers are in the ratio 5 : 6 . If 8 is subtracted from each of the numbers , the ratio becomes 4 : 5 . Find the numbers .
Answer:
Let the two numbers be x and y.
So,
Now, when 8 is subtracted from each of the numbers, then
Multiplying (i) with 4 and (ii) with 5, we get
24x − 20y = 0 .....(iii)
25x − 20y = 40 .....(iv)
Subtracting (iii) from (iv), we get
x = 40
Putting x = 40 in (i), we get
240 − 5y = 0
⇒ y = 48
Thus, the two numbers are 40 and 48.
Page No 145:
Question 10:
A two-digit number is obtained by either multiplying the sum of the digits by 8 and then subtracting 5 or by multiplying the difference of the digits by 16 and then adding 3 . Find the number .
Answer:
Let the digits of the two digit number be x and y. So, the two digit number will be 10x + y.
Now, according to the given condition the number is obtained in two ways.
Case I: 8(x + y) − 5 = 10x + y
⇒ 8x + 8y − 5 = 10x + y
⇒ 2x −7y = −5 .....(1)
Case II: 16(x − y) + 3 = 10x + y
⇒ 16x − 16y + 3 = 10x + y
⇒ 6x − 17y = −3 .....(2)
Multiplying (1) by 3, we get
6x − 21y = −15 .....(3)
Subtracting (2) from (3), we get
− 4y = −12
⇒ y = 3
Putting y = 3 in (1), we get
2x − 21 = −5
⇒ 2x = 16
⇒ x = 8
So, the required number is 10x + y = 10 × 8 + 3 = 83.
Page No 147:
Question 1:
The numerator of a fraction is 4 less than the denominator. If the numerator is decreased by 2 and denominator is increased by 1, then the denominator is eight times the numerator. Find the fraction.
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
The numerator of the fraction is 4 less the denominator. Thus, we have
If the numerator is decreased by 2 and denominator is increased by 1, then the denominator is 8 times the numerator. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
Subtracting the second equation from the first equation, we get
Substituting the value of x in the first equation, we have
Hence, the fraction is.
Page No 147:
Question 2:
A fraction becomes 9/11 if 2 is added to both numerator and the denominator. If 3 is added to both the numerator and the denominator it becomes 5/6. Find the fraction.
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
If 2 is added to both numerator and the denominator, the fraction becomes. Thus, we have
If 3 is added to both numerator and the denominator, the fraction becomes. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the fraction is.
Page No 147:
Question 3:
If we add 1 to the numerator and subtract 1 from the denominator, a fraction becomes 1. It also becomes 1/2 if we only add 1 to the denominator. What is the fraction?
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
If 1 is added to the numerator and 1 is subtracted from the denominator, the fraction becomes. Thus, we have
If 1 is added to the denominator, the fraction becomes. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the fraction is.
Page No 147:
Question 4:
If the numerator of a fraction is multiplied by 2 and the denominator is reduced by 5 the fraction becomes 6/5. And, if the denominator is doubled and the numerator is increased by 8, the fraction becomes 2/5. find the fraction.
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
If the numerator is multiplied by 2 and the denominator is reduced by 5, the fraction becomes. Thus, we have
If the denominator is doubled and the numerator is increased by 8, the fraction becomes. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the fraction is.
Page No 147:
Question 5:
When 3 is added to the denominator and 2 is subtracted from the numerator a fraction becomes 1/4. And when 6 is added to numerator and the denominator is multiplied by 3, it becomes 2/3. Find the fraction.
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
If 3 is added to the denominator and 2 is subtracted from the numerator, the fraction becomes. Thus, we have
If 6 is added to the numerator and the denominator is multiplied by 3, the fraction becomes. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the fraction is.
Page No 147:
Question 6:
A fraction becomes 1/3 when 2 is subtracted from the numerator and it becomes 1/2 when 1 is subtracted from the denominator. Find the fraction.
Answer:
Let the numerator of the fraction be x and the denominator be y.
According to the question,
Page No 147:
Question 7:
The sum of the numerator and denominator of a fraction is 4 more than twice the numerator. If the numerator and denominator are increased by 3, they are in the ratio 2 : 3. Determine the fraction.
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
The sum of the numerator and denominator of the fraction is 4 more than twice the numerator. Thus, we have
If the numerator and denominator are increased by 3, they are in the ratio 2:3. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the fraction is.
Page No 147:
Question 8:
The sum of the numerator and denominator of a fraction is 3 less than twice the denominator. If the numerator and denominator are decreased by 1, the numerator becomes half the denominator. Determine the fraction.
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
The sum of the numerator and denominator of the fraction is 3 less than twice the denominator. Thus, we have
If the numerator and denominator are decreased by 1, the numerator becomes half the denominator. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the fraction is.
Page No 147:
Question 9:
The sum of the numerator and denominator of a fraction is 12. If the denominator is increased by 3, the fraction becomes 1/2. Find the fraction.
Answer:
Let the numerator and denominator of the fraction be x and y respectively. Then the fraction is
The sum of the numerator and denominator of the fraction is 12. Thus, we have
If the denominator is increased by 3, the fraction becomes. Thus, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the fraction is.
Page No 149:
Question 1:
Ten years later, A will be twice as old as B and five years ago, A was three times as old as B. What are the present ages of A and B?
Answer:
Let the present age of A be x years and the present age of B be y years.
After 10 years, A’s age will beyears and B’s age will beyears. Thus using the given information, we have
Before 5 years, the age of A wasyears and the age of B wasyears. Thus using the given information, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the present age of A isyears and the present age of B isyears.
Page No 149:
Question 2:
Five years ago, Nuri was thrice as old as Sonu. Ten years later, Nuri will be twice as old as Sonu. How old are Nuri and Sonu?
Answer:
Let the present age of Nuri be x years and the present age of Sonu be y years.
After 10 years, Nuri’s age will be(x + 10) years and the age of Sonu will be(y + 10) years. Thus using the given information, we have
Before 5 years, the age of Nuri was(x – 5)years and the age of Sonu was(y – 5)years. Thus using the given information, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the present age of Nuri isyears and the present age of Sonu isyears.
Page No 149:
Question 3:
Six years hence a man's age will be three times the age of his son and three years ago he was nine times as old as his son. Find their present ages.
Answer:
Let the present age of the man be x years and the present age of his son be y years.
After 6 years, the man’s age will beyears and son’s age will beyears. Thus using the given information, we have
Before 3 years, the age of the man wasyears and the age of son’s wasyears. Thus using the given information, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the present age of the man isyears and the present age of son isyears.
Page No 149:
Question 4:
Ten years ago, a father was twelve times as old as his son and ten years hence, he will be twice as old as his son will be then. Find their present ages.
Answer:
Let the present age of father be x years and the present age of his son be y years.
After 10 years, father’s age will beyears and son’s age will beyears. Thus using the given information, we have
Before 10 years, the age of father wasyears and the age of son wasyears. Thus using the given information, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the present age of father isyears and the present age of son isyears.
Page No 149:
Question 5:
Father's age is three times the sum of age of his two children. After 5 years his age will be twice the sum of ages of two children. Find the age of father.
Answer:
Let the present age of father be x years and the present ages of his two children’s be y and z years.
The present age of father is three times the sum of the ages of the two children’s. Thus, we have
After 5 years, father’s age will beyears and the children’s age will beandyears. Thus using the given information, we have
So, we have two equations
Here x, y and z are unknowns. We have to find the value of x.
Substituting the value offrom the first equation in the second equation, we have
By using cross-multiplication, we have
Hence, the present age of father isyears.
Page No 149:
Question 6:
Two years ago, a father was five times as old as his son. Two year later, his age will be 8 more than three times the age of the son. Find the present ages of father and son.
Answer:
Let the present age of father be x years and the present age of his son be y years.
After 2 years, father’s age will beyears and the age of son will beyears. Thus using the given information, we have
Before 2 years, the age of father wasyears and the age of son wasyears. Thus using the given information, we have
So, we have two equations
Here x and y are unknowns. We have to solve the above equations for x and y.
By using cross-multiplication, we have
Hence, the present age of father isyears and the present age of son isyears.
Page No 149:
Question 7:
The ages of two friends Ani and Biju differ by 3 years. Ani's father Dharma is twice as old as Ani and Biju as twice as old as his sister Cathy. The ages of Cathy and Dharam differ by 30 years. Find the ages of Ani and Biju.
Answer:
Let the present ages of Ani, Biju, Dharam and Cathy be x, y, z and t years respectively.
The ages of Ani and Biju differ by 3 years. Thus, we have
Dharam is twice as old as Ani. Thus, we have
Biju is twice as old as Cathy. Thus, we have
The ages of Cathy and Dharam differ by 30 years. Clearly, Dharam is older than Cathy. Thus, we have
So, we have two systems of simultaneous equations
(i)
(ii)
Here x, y, z and t are unknowns. We have to find the value of x and y.
(i) By using the third equation, the first equation becomes
From the fourth equation, we have
Hence, we have
Using the second equation, we have
From the first equation, we have
Hence, the age of Ani isyears and the age of Biju isyears.
(ii) By using the third equation, the first equation becomes
From the fourth equation, we have
Hence, we have
Using the second equation, we have
From the first equation, we have
Hence, the age of Ani isyears and the age of Biju isyears.
Note that there are two possibilities.
Page No 149:
Question 8:
Two years ago, Salim was thrice as old as his daughter and six years later , he will be four years older than twice her age . How old are they now ?
Answer:
Let the present ages of Salim be x years and that of her daughter be y years.
Two years ago, the age of Salim was (x − 2) years and that of her daughter was (y − 2).
It is given that Salim was thrice as old as her daughter two years ago. So,
x − 2 = 3(y − 2)
⇒ x − 2 = 3y − 6
⇒ x − 3y = −4 .....(i)
Six years later, the age of Salim will be (x + 6) and that of her daughter will be (y + 6).
∴ x + 6 = 2(y + 6) + 4
⇒ x − 2y = 10 .....(ii)
Subtracting (ii) from (i), we get
−y = −14
⇒ y = 14
Putting y = 14 in (ii), we get
x − 28 = 10
⇒ x = 38
Hence, the present age of Salim is 38 years and that of her daughter is 14 years.
Page No 149:
Question 9:
The age of the father is twice the sum of the ages of his two children . After 20 years , his age will be eual to the sum of the ages of his children . Find the age of the father.
Answer:
Let the present age of the father be x years and the sum of the present ages of his two children be y years.
Now according to the given conditions,
Case I: x = 2y
⇒ x − 2y = 0 .....(i)
Case II: After 20 years, the age of the father will be (x + 20) years and the sum of the ages of the two children will be y + 20 + 20 = (y + 40) years.
So, x + 20 = y + 40
⇒ x − y = 20 .....(ii)
Subtracting (ii) from (i), we get
− y = −20
⇒ y = 20
Putting y = 20 in (i), we get
x − 40 = 0
⇒ x = 40
Hence, the present age of the father is 40 years.
Page No 156:
Question 1:
Point A and B are 70 km. a part on a highway. A car starts from A and another car starts from B simultaneously. If they travel in the same direction, they meet in 7 hours, but if the travel towards each other, the meet in one hour. Find the speed of the two cars.
Answer:
We have to find the speed of car
Let and be two cars starting from pointsand respectively. Let the speed of car be x km/hr and that of carbe y km/hr.
Case I: When two cars move in the same directions:
Suppose two cars meet at point, Then,
Distance travelled by car
Distance travelled by car
It is given that two cars meet in 7 hours.
Therefore, Distance travelled by car X in hours = km
Distance traveled by car y in 7 hours = km
Clearly
Dividing both sides by common factor 7 we get,
Case II : When two cars move in opposite direction
Suppose two cars meet at point. Then,
Distance travelled by car,
Distance travelled by car.
In this case, two cars meet in 1 hour
Therefore Distance travelled by car X in1 hour km
Distance travelled by car Y in 1 hour km
From the above clearly,
...(ii)
By solving equation (i) and (ii), we get
Substituting in equation (ii) we get
Hence, the speed of car starting from point A is
The speed of car starting from point B is.
Page No 156:
Question 2:
The boat goes 30 km upstream and 44 km downstream in 10 hours. In 13 hours, it can go 40 km upstream and 55 km downstream. Determine the speed of stream and that of the boat in still water.
Answer:
Let the speed of the boat in still water be x km/hr and the speed of the stream be y km/hr
Speed upstream =km/hr
Speed down stream =km/hr
Now,
Time taken to cover 30 km upstream = hrs
Time taken to cover 44 km down stream = hrs
But total time of journey is 10 hours
Time taken to cover 40 km upstream=
Time taken to cover 55 km down stream =
In this case total time of journey is given to be 13 hours
Therefore, ...(ii)
Putting = u and in equation and we get
Solving these equations by cross multiplication we get
and
Now,
By solving equation and we get ,
Substituting in equation we get ,
Hence, speed of the boat in still water is
Speed of the stream is
Page No 156:
Question 3:
A person rowing at the rate of 5 km/h in still water , takes thrice as much time in going 40 km upstream as in going 40 km downstream . Find the speed of the stream .
Answer:
Speed of the boat in still water = 5 km/h
Let the speed of stream = x km/h
∴ Speed of boat upstream = (5 − x) km/h
Speed of boat downstream = (5 + x) km/h
Time taken to row 40 km upstream =
Time taken to row 40 km downstream =
According to the given condition,
Therefore, the speed of the stream is 2.5 km/h.
Page No 156:
Question 4:
A man travels 600 km partly by train and partly by car. If the covers 400 km by train and the rest by car, it takes him 6 hours 30 minutes. But, if the travels 200 km by train and the rest by car, he takes half an hour longer. Find the speed of the train and that of the car.
Answer:
Let the speed of the train be x km/hr that of the car be y km/hr, we have the following cases:
Case I: When a man travels 600Km by train and the rest by car
Time taken by a man to travel 400 Km by train =
Time taken by a man to travel (600-400) =200Km by car =hrs
Total time taken by a man to cover 600Km =
It is given that total time taken in 8 hours
Case II: When a man travels 200Km by train and the rest by car
Time taken by a man to travel 200 Km by train =
Time taken by a man to travel (600-200) = 400 Km by car
In this case, total time of the journey in 6 hours 30 minutes + 30 minutes that is 7 hours,
...(ii)
Putting and, , the equations and reduces to
Multiplying equation (iii) by 6 the above system of equation becomes
Substituting equation and, we get
Putting in equation, we get
Now
and
Hence, the speed of the train is,
The speed of the car is.
Page No 156:
Question 5:
Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours. Find her speed of rowing in still water and the speed of the current.
Answer:
Let the speed of rowing in still water be x km/hr and the speed of the current be y km/hr
Speed upstream
Speed downstream
Now,
Time taken to cover km down stream =
Time taken to cover km upstream =
But, time taken to cover km downstream in
Time taken to cover km upstream in 2 hours
...(i)
By solving these equation (i) and (ii) we get
Substitute in equation (i)we get
Hence, the speed of rowing in still water is,
The speed of current is .4 km/ hr
Page No 156:
Question 6:
A motor boat can travel 30 km upstream and 28 km downstream in 7 hours . It can travel 21 km upstream and return in 5 hours . Find the speed of the boat in still water and the speed of the upstream .
Answer:
Let the speed of the boat in still water be x km/h and the speed of the stream be y km/h.
Speed of boat upstream = x − y
Speed of boat downstream = x + y
It is given that, the boat travels 30 km upstream and 28 km downstream in 7 hours.
Also, the boat travels 21 km upstream and return in 5 hours.
Let .
So, the equation becomes
Multiplying (i) by 21 and (ii) by 30, we get
Solving (iii) and (iv), we get
and
But,
So,
Solving these two equations, we get
x = 10 and y = 4
So, the speed of boat in still water = 10 km/h and speed of stream = 4 km/h.
Page No 156:
Question 7:
Abdul travelled 300 km by train and 200 km by taxi, it took him 5 hours 30 minutes. But if he travels 260 km by train and 240 km by taxi he takes 6 minutes longer. Find the speed of the train and that of the taxi.
Answer:
Let the speed of the train be x km/hour that of the taxi be y km/hr, we have the following cases
Case I: When Abdul travels 300 Km by train and the 200 Km by taxi
Time taken by Abdul to travel 300 Km by train =
Time taken by Abdul to travel 200 Km by taxi =
Total time taken by Abdul to cover 500 Km =
It is given that total time taken in 5 hours 30 minutes
Case II: When Abdul travels 260 Km by train and the 240 km by taxi
Time taken by Abdul to travel 260 Km by train =
Time taken by Abdul to travel 240 Km by taxi =
In this case total time of the journey is 5 hours 36 minutes
Putting and, , the equations and reduces to
Multiplying equation by 6 the above system of equation becomes
Subtracting equation from we get
Putting in equation, we get
Now
and
Hence, the speed of the train is ,
The speed of the taxi is .
Page No 156:
Question 8:
Places A and B are 100 km apart on a highway. One car starts from A and another from B at the same time. If the cars travel in the same direction at different speeds, they meet in 5 hours. If they travel towards each other, they meet in 1 hour. What are the speeds of two cars.
Answer:
Let x and y be two cars starting from points A and B respectively.
Let the speed of the car X be x km/hr and that of the car Y be y km/hr.
Case I: When two cars move in the same directions:
Suppose two cars meet at point Q, then,
Distance travelled by car X=AQ
Distance travelled by car Y=BQ
It is given that two cars meet in 5 hours.
Distance travelled by car X in 5 hours =km AQ=
Distance travelled by car Y in 5 hours =km BQ=
Clearly AQ-BQ = AB
Both sides divided by 5, we get
Case II: When two cars move in opposite direction
Suppose two cars meet at point P, then,
Distance travelled by X car X=AP
Distance travelled by Y car Y=BP
In this case, two cars meet in 1 hour
Therefore,
Distance travelled by car y in1 hours = km
Distance travelled by car y in 1 hours = km
By solving (i) and (ii) we get,
By substituting in equation (ii), we get
Hence, speed of car X is , speed of car Y is.
Page No 156:
Question 9:
A train covered a certain distance at a uniform speed. If the train could have been 10 km/hr. faster, it would have taken 2 hours less than the scheduled time. And, if the train were slower by 10 km/hr; it would have taken 3 hours more than the scheduled time. Find the distance covered by the train.
Answer:
Let the actual speed of the train be and the actual time taken by y hours. Then,
Distance covered=
If the speed is increased by, then time of journey is reduced by 2 hours
when speed is , time of journey is
Distance covered=
When the speed is reduced by, then the time of journey is increased by when speed is, time of journey is
Distance covered=
Thus, we obtain the following system of equations:
By using cross multiplication, we have
Putting the values of x and y in equation (i), we obtain
Distance=
Hence, the length of the journey is .
Page No 156:
Question 10:
While covering a distance of 30 km. Ajeet takes 2 hours more than Amit. If Ajeet doubles his speed, he would take 1 hour less than Amit. Find their speeds of walking.
Answer:
Let the speed of Ajeet and Amit be x Km/hr respectively. Then,
Time taken by Ajeet to cover
Time taken by Amit to cover
By the given conditions, we have
If Ajeet doubles his speed, then speed of Ajeet is
Time taken by Ajeet to cover
Time taken by Amit to cover
According to the given condition, we have
...(ii)
Putting and, in equation (i) and (ii), we get
Adding equations (iii) and (iv), we get
Putting in equation (iii), we get
Now,
and
Hence, the speed of Ajeet is
The speed of Amit is
Page No 156:
Question 11:
A man walks a certain distance with certain speed. If he walks 1/2 km an hour faster, he takes 1 hour less. But, if he walks 1 km an hour slower, he takes 3 more hours. Find the distance covered by the man and his original rate of walking.
Answer:
Let the actual speed of the train be x Km/hr and the actual time taken by y hours. Then,
Distance covered=
If the speed is increased by, then time of journey is reduced by 1 hour i.e., when speed is , time of journey is
Distance covered= km
...(ii)
When the speed is reduced by, then the time of journey is increased by i.e., when speed is, time of journey is
Distance covered =
Thus we obtain the following equations
By using elimination method, we have
Putting the value in equation (iii) we get
Putting the value of x and y in equations (i) we get
Distance covered =
=
Hence, the distance is,
The speed of walking is .
Page No 163:
Question 1:
In a rectangle, if the length is increased by 3 meters and breadth is decreased by 4 meters, the area of the rectangle is reduced by 67 square meters. If length is reduced by 1 meter and breadth is increased by 4 meters, the area is increased by 89 Sq. meters. Find the dimensions of the rectangle.
Answer:
Let the length and breadth of the rectangle be and units respectively
Then, area of rectangle = square units
If the length is increased by meters and breath is reduced each by square meters the area is reduced by square units
Therefore,
Then the length is reduced by meter and breadth is increased by meter then the area is increased by square units
Therefore,
Thus, we get the following system of linear equation
By using cross multiplication we have
and
Hence, the length of rectangle ismeter,
The breath of rectangle is meter.
Page No 163:
Question 2:
ABCD is a cyclic quadrilateral such that ∠A = (4y + 20)°, ∠B = (3y − 5)°, ∠C = (−4x)° and ∠D = (7x + 5)°. Find the four angles.
Answer:
We know that the sum of the opposite angles of cyclic quadrilateral is .in the cyclic quadrilateral angles and and angles and pairs of opposite angles
Therefore
and
By substituting and we get
Divide both sides of equation by 4 we get
By substituting and we get
By multiplying equation by 3 we get
By subtracting equation from we get
By substituting in equation we get
The angles of a cyclic quadrilateral are
Hence the angles of quadrilateral are
Page No 163:
Question 3:
Yash scored 40 marks in a test, getting 3 marks for each right answer and losing 1 mark for each wrong answer. Had 4 marks been awanded for each correct answer and 2 marks been deducted for each incorrect answer, the Yash would have scored 50 marks. How many question were there in the test?
Answer:
Let take right answer will beand wrong answer will be .
Hence total number of questions will be
If yash scored marks in atleast getting marks for each right answer and losing mark for each wrong answer then
If 4 marks awarded for each right answer and 2 marks deduced for each wrong answer the he scored 50 marks
By multiplying equation by 2 we get
By subtracting from we get
Putting in equation we have
Total number question will be
Hence, the total number of question is .
Page No 163:
Question 4:
The car hire charges in a city comprise of a fixed charges together with the charge for the distance covered. For a journey of 12 km, the charge paid is Rs 89 and the journey of 20 km, the charge paid is Rs 145. What will a person have to pay for travelling a distance of 30 km?
Answer:
Let the fixed charges of car be per km and the running charges be km/hr
According to the given condition we have
Putting in equation we get
Therefore, Total charges for travelling distance of km
= Rs
Hence, A person have to pay for travelling a distance of km.
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Question 5:
A part of monthly hostel charges in a college are fixed and the remaining depend on the number of days one has taken food in the mess. When a student A takes foods for 20 days, he has to pay Rs 1000 as hostel charges whereas a students B, who takes food for 26 days, pays Rs 1180 as hostel charges. Find the fixed charge and the cost of food per day.
Answer:
Let the fixed charges of hostel be and the cost of food charges be per day
According to the given condition we have,
Subtracting equation from equation we get
Putting in equation we get
Hence, the fixed charges of hostel is .
The cost of food per day is .
Page No 163:
Question 6:
The larger of two supplementary angles exceeds the smaller by 18 degrees. Find them.
Answer:
We know that the sum of supplementary angles will be.
Let the longer supplementary angles will be.
Then,
If larger of supplementary angles exceeds the smaller by degree, According to the given condition. We have,
Substitute in equation, we get,
Put equation, we get,
Hence, the larger supplementary angle is ,
The smaller supplementary angle is.
Page No 163:
Question 7:
Meena went to a bank to withdraw Rs 2000. She asked the cashier to give her Rs 50 and Rs 100 notes only. Meena got 25 notes in all. Find how many notes Rs 50 and Rs 100 she received.
Answer:
Let be the notes of and notes will be
If Meena ask for and notes only, then the equation will be,
Divide both sides by then we get,
If Meena got 25 notes in all then the equation will be,
By subtracting the equation from we get,
Substituting in equation, we get
Therefore and
Hence, Meena has notes of and notes of
Page No 163:
Question 8:
A shopkeeper gives books on rent for reading . She takes a fixed charge for the first two days, and an additional charge for each day thereafter . Latika paid â¹22 for a book kept for 6 days, while Anand paid â¹16 for the book kept for four days . Find the fixed charges and charge for each extraday.
Answer:
Let the fixed charge for first two days be â¹x and the additional charge for each day extra be â¹y.
It is given that Latika kept the book for 6 days and paid â¹22.
So,
Fixed charge for the first 2 days + Additional charge for 4 days = â¹22
∴ x + 4y = 22 .....(i)
Anand kept the book for 4 days and paid â¹16. So,
Fixed charge for the first 2 days + Additional charge for 2 days = â¹16
∴ x + 2y = 16 .....(ii)
Subtracting (ii) from (i), we get
2y = 6
⇒ y = 3
Putting y = 3 in (i), we get
x + 12 = 22
⇒ x = 10
Thus, the fixed charge is â¹10 and the additional charge for each extraday is â¹3.
Page No 164:
Question 9:
2 women and 5 men can together finish a piece of embroidery in 4 days, while 3 women and 6 men can finish it in 3 days. Find the time taken by 1 woman alone to finish the embroidery, and that taken by 1 man alone.
Answer:
1 women alone can finish the work in days and 1 man alone can finish it in days .then
One woman one day work=
One man one days work =
2 women’s one days work=
5 man’s one days work =
Since 2 women and 5 men can finish the work in 4 days
3 women and 6 men can finish the work in 3 days
Putting and in equation and we get
By using cross multiplication we have
Now ,
Hence, the time taken by 1 woman alone to finish the embroidery is,
The time taken by 1 man alone to finish the embroidery is .
Page No 164:
Question 10:
There are two examination rooms A and B. If 10 candidates are sent from A to B, the number of students in each room is same. If 20 candidates are sent from B to A, the number of students in A is double the number of students in B. Find the number of students in each room.
Answer:
Let us take the A examination room will be x and the B examination room will be y
If 10 candidates are sent from A to B, the number of students in each room is same. According to the above condition equation will be
If 20 candidates are sent from B to A, the number of students in A is double the number of students in B, then equation will be,
By subtracting the equationfromwe get,
Substituting in equation, we get
Hence candidates are in A examination Room,
candidates are in B examination Room.
Page No 164:
Question 11:
A railway half ticket costs half the full fare and the reservation charge is the same on half ticket as on full ticket. One reserved first class ticket from Mumbai to Ahmedabad costs Rs 216 and one full and one half reserved first class tickets cost Rs 327. What is the basic first class full fare and what is the reservation charge?
Answer:
Let take first class full of fare is Rs and reservation charge is Rs per ticket
Then half of the ticket as on full ticket =
According to the given condition we have
Multiplying equation by 2 we have
Subtracting from we get
Putting in equation we get
Hence, the basic first class full fare is
The reservation charge is .
Page No 164:
Question 12:
A shopkeeper sells a saree at 8% profit and a sweater at 10% discount, thereby getting a sum of â¹1008. If she had sold the saree at 10% profit and the sweater at 8% discount , she would have got â¹ 1028 . Find the cost price of the saree and the list price (price before discount) of the sweater.
Answer:
Let the CP of saree be â¹x and the list price of sweater be â¹y.
Case I: When saree is sold at 8% profit and sweater at 10% discount.
SP = CP + Profit
⇒ SP of saree = x + =
SP of sweater = List price − Discount
⇒ SP of sweater = =
Total sum received by the shopkeeper = â¹1008
⇒ + = 1008
⇒ 108x + 90y = 100800
⇒ 6x + 5y = 5600 .....(i)
Case II: When saree is sold at 10% profit and sweater at 8% discount.
⇒ SP of saree = x + =
SP of sweater = List price − Discount
⇒ SP of sweater = =
Total sum received by the shopkeeper = â¹1028
⇒ + = 1028
⇒ 110x + 92y = 102800 .....(ii)
Multiplying (i) by 110 and (ii) by 6, we get
660x + 550y = 616000 .....(iii)
660x + 552y = 616800 .....(iv)
Subtracting (iii) from (iv), we get
2y = 800
⇒ y = 400
Putting y = 400 in (i), we get
6x + 2000 = 5600
⇒ 6x = 5600 − 2000 = 3600
⇒ x = 600
Hence, CP of saree = â¹600 and list price of sweater = â¹400.
Page No 164:
Question 13:
In a competitive examination , one mark is awarded for each correct answer while 1/2 mark is deducted for everey wrong answer . Jayanti answered 120 questions and got 90 marks. How many questions did she answer correctly.
Answer:
Let the number of correct answers be x and the number of wrong answers be y.
Total questions Jayanthi answered = 120
So, x + y = 120 .....(i)
Now, marks obtained for answering correctly = 1 × x = x
Marks deducted for answering incorrectly = =
Total marks obtained = .....(ii)
Subtracting (ii) from (i), we get
Putting y = 20 in (i), we get
x + 20 = 120
⇒ x = 100
Thus, Jayanti answered 100 questions correctly.
Page No 164:
Question 1:
Write the value of k for which the system of equations x + y − 4 = 0 and 2x + ky − 3 = 0 has no solution.
Answer:
The given system of equations is
.
For the equations to have no solutions
By cross multiplication we get,
Hence, the value of k is when system equations has no solution.
Page No 164:
Question 2:
Write the value of k for which the system of equations has infinitely many solutions.
Answer:
The given systems of equations are
For the equations to have infinite number of solutions,
By cross Multiplication we get,
Hence the value of k is when equations has infinitely many solutions.
Page No 164:
Question 3:
Write the value of k for which the system of equations 3x − 2y = 0 and kx + 5y = 0 has infinitely may solutions.
Answer:
The given equations are
For the equations to have infinite number of solutions,
Therefore,
By cross multiplication we have
Hence, the value of k for the system of equation and is.
Page No 164:
Question 4:
Write the value of k for which the system of equations x + ky = 0, 2x − y = 0 has unique solution.
Answer:
The given equations are
For unique solution
For all real values of k, except the equations have unique solutions.
Page No 164:
Question 5:
Write the set of values of a and b for which the following system of equations has infinitely many solutions.
Answer:
The given equations are
For the equations to have infinite number of solutions,
Therefore
Let us take
By dividing both the sides by 7 we get,
By multiplying equations by 2 we get
Substituting from we get
Subtracting in equation we have
Hence, the value of when system of equations has infinity many solutions.
Page No 164:
Question 6:
For what value of k, the following pair of linear equation has infinitely many solutions?
Answer:
The given equations are
For the equations to have infinite number of solutions
Let us take
Hence, the value of when the pair of linear equations has infinitely many solutions.
Page No 165:
Question 7:
Write the number of solution of the following pair of linear equations:
x + 2y − 8 = 0
2x + 4y = 16
Answer:
The given equations are
Every solution of the second equation is also a solution of the first equation.
Hence, there are, the system equation is consistent.
Page No 165:
Question 8:
Write the number of solutions of the following pair of linear equations:
x + 3y − 4 = 0
2x + 6y = 7
Answer:
The given linear pair of equations are
If then
Hence, the number of solutions of the pair of linear equation is.
Therefore, the equations have no solution.
Page No 165:
Question 1:
The pair of equations y = 0 and y = –7 has _________ solution.
Answer:
The equation y = 0 is the x-axis and y = –7 is the line parallel to x-axis.
Therefore, both the lines are parallel lines.
Hence, the pair of equations y = 0 and y = –7 has no solution.
Page No 165:
Question 2:
The pair of equations x = a and y = b has solution ________.
Answer:
The equation x = a is the line parallel to y-axis and y = b is the line parallel to x-axis.
âTherefore, both the lines intersect each other.
The point of intersection is x = a and y = b i.e. (a, b).
Hence, the pair of equations x = a and y = b has solution (a, b).
Page No 165:
Question 3:
If the pair of equations 3x + 2ky = 2 and 2x + 5y + 1 = 0 has no solution, then k = _________.
Answer:
If the system of equations has no solution, then .
Since, the system of equations 3x + 2ky = 2 and 2x + 5y + 1 = 0 has no solution
Therefore,
Hence, k =
Page No 165:
Question 4:
If a pair of linear equations is consistent, then the lines representing them are either _______ or ________.
Answer:
If a pair of linear equations is consistent, then two case arises:
Case 1: When the lines are coincident, they have infinitely many solutions.
Case 2: When the lines are intersecting, they have a unique solution.
Hence, If a pair of linear equations is consistent, then the lines representing them are either coincident or intersecting.
Page No 165:
Question 5:
There is (are) ________ value(s) of c for which the pair of equations cx – y = 2 and 6x – 2y = 3 have infinitely many solutions.
Answer:
If the system of equations has infinitely many solutions, then .
Since, the system of equations cx – y = 2 and 6x – 2y = 3 has infinitely many solutions
Therefore,
Therefore, for no value of c the pair of equations cx – y = 2 and 6x – 2y = 3 have infinitely many solutions.
Hence, there is (are) no value(s) of c for which the pair of equations cx – y = 2 and 6x – 2y = 3 have infinitely many solutions.
Page No 165:
Question 6:
If a pair of linear equations is consistent with a unique solution, then the lines representing them are _______.
Answer:
If a pair of linear equations is consistent, then two case arises:
Case 1: When the lines are coincident, they have infinitely many solutions.
Case 2: When the lines are intersecting, they have a unique solution.
Hence, if a pair of linear equations is consistent with a unique solution, then the lines representing them are intersecting.
Page No 165:
Question 7:
The pair of equations λx + 3y = 7, 2x + 6y = 14 will have infinitely many solutions for λ = ________.
Answer:
If the system of equations has infinitely many solutions, then .
Since, the system of equations λx + 3y = 7, 2x + 6y = 14 has infinitely many solutions
Therefore,
Hence, the pair of equations λx + 3y = 7, 2x + 6y = 14 will have infinitely many solutions for λ = 1 .
Page No 165:
Question 8:
If the pair of equations 2x + 3y – 5 = 0 and px – 6y – 8 = 0 has a unique solution for all real values of p except _______.
Answer:
If the system of equations has a unique solution, then .
Since, the system of equations 2x + 3y – 5 = 0 and px – 6y – 8 = 0 has a unique solution
Therefore,
Hence, if the pair of equations 2x + 3y – 5 = 0 and px – 6y – 8 = 0 has a unique solution for all real values of p except –4.
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Question 9:
If the lines represented by the equations 3x – y – 5 = 0 and 6x – 2y – p = 0 are parallel, then p is equal to ________.
Answer:
If the system of equations has no solution, i.e., they are parallel, then .
Since, the system of equations 3x – y – 5 = 0 and 6x – 2y – p = 0 are parallel
Therefore,
Hence, if the lines represented by the equations 3x – y – 5 = 0 and 6x – 2y – p = 0 are parallel, then p is equal to all real values except 10.
Page No 165:
Question 10:
If x = a, y = b is the solution of the pair of equations x – y = 2 and x + y = 4, then a = _______ and b = _______.
Answer:
Since, x = a, y = b is the solution of the pair of equations x – y = 2 and x + y = 4
Therefore, x = a, y = b satisfies the equations x – y = 2 and x + y = 4.
Hence, a = 3 and b = 1.
Page No 165:
Question 11:
If one equation of a pair of dependent linear equations is 5x – 7y + 2 = 0, then the second equation is given by _______.
Answer:
To get the dependent linear equation, multiply the given equation by any non-zero integer.
If we multiply the given equation by any non-zero integer a, we get
5ax – 7ay + 2a = 0
Hence, the second equation is given by 5ax – 7ay + 2a = 0, where a is any non-zero integer.
Page No 165:
Question 12:
If the pair of equations ax + 2y = 7 and 3x + by = 16 represent parallel lines, then ab = ________.
Answer:
If the system of equations has no solution, i.e., they are parallel, then .
Since, the system of equations ax + 2y = 7 and 3x + by = 16 represent parallel lines
Therefore,
Hence, If the pair of equations ax + 2y = 7 and 3x + by = 16 represent parallel lines, then ab = 6.
Page No 165:
Question 13:
The line 4x + 3y – 12 = 0 cuts the coordinate axes at A and B. The area of ΔOAB is _________.
Answer:
The given equation is 4x + 3y – 12 = 0 ...(i)
Solving equation (i), we get
When x = 0, y = 4
When x = 3, y = 0
x | 0 | 3 |
y | 4 | 0 |
On plotting these points on a graph, we get
We can see that OA = 3 units and OB = 4 units
Area of ΔOAB =
=
= 6
Hence, the area of ΔOAB is 6 square units.
Page No 165:
Question 14:
If 2x+y = 2x–y = , then x = _______ and y = _______.
Answer:
Given: 2x+y = 2x–y =
Now,
Hence, x = and y = 0.
Page No 165:
Question 15:
The system of equations ax + 3y = 1, –12x + ay = 2 has ________ for all real values of a.
Answer:
The given system of equations are:
ax + 3y = 1 ...(i)
–12x + ay = 2 ...(ii)
Now,
Hence, the system of equations ax + 3y = 1, –12x + ay = 2 has a unique solution for all real values of a.
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