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Numerical Applications

Solve problems on the concept of average speed

Age of a person, hours in a day, duration of a cricket match, etc.– everything represents time. There are two main objects that tell us time: clock and calendar.
Our ancestors used to calculate time by observing the position of the Sun. But that would not be possible during cloudy days and rainy seasons.
In ancient times, people used different types of time-telling instruments like shadow clock, rope clock, water clock, candle clock and sand clock to determine time.

 
Units of time

Seconds, minutes, hours, days, weeks, months and years are different units of time. We can convert one unit into another by using the relations between them.
Let us learn in detail about the units of time and their relations.

The smallest possible unit of time is second. 60 seconds make 1 minute and 60 minutes make 1 hour.
i.e., 1 minute = 60 seconds and 1 hour = 60 minutes
In other words, 1 second = 160 minutes and 1 minute = 160 hour
Using the above two relations, let us find out the relation between hours and seconds.
We know that 1 hour = 60 minutes
                            = 60 times 60 seconds            [because  1 minute = 60 seconds]
                            = 3600 seconds
therefore 1 hour = 3600 seconds

There are 24 hours in a day, so we can convert days in terms of minutes or seconds as shown below:
1 day = 24 hours
          = 24 times 60 minutes         [because  1 hour = 60 minutes]
          = 1440 minutes
          = 1440 times 60 seconds    [because  1 minute = 60 seconds]
          = 86400 seconds
i.e., 1 day = 24 times 60 minutes = 24 times 60 times 60 seconds  

So, we have the following:
1 minute = 60 seconds
1 second = 160 minutes
1 hour = 60 minutes = 3600 seconds
1 minute = 160 hour
1 second = 13600 hour
1 day = 24 times 60 minutes = 24 times 60 times 60 seconds  
 

Now, using the given relations, let us try to convert 18 minutes into seconds.
We know that 1 minute = 60 seconds
In order to convert 18 minutes into seconds, we need to multiply 18 by 60.
therefore 18 minutes = 18 times 60 minutes
                      = 1080 minutes

Now, let us convert 780 minutes into hours.
We know that 1 minute = 160 hour
In order to convert 780 minutes into hours, let us multiply 780 by 160.
therefore 780 minutes = 780 times 160 hours
                              = 78060 hours
                              = 13 hours

 
24 hour clock
We usually denote time from 12 mid-night to 12 noon as A.M. (Latin: Ante meridiem) and the time from 12 noon to 12 mid-night as P.M. (Latin: Post meridiem).
Look at the following times:
14:40 hours and 20:00 hours
Such representation of times is shown by a 24 hour clock.
In a 24 hour clock, 12 A.M. is represented as 00:00 hours and 12 P.M. is represented as 12:00 hours.
The given tables shows the different formats of time (in A.M.) represented by a 12 hour clock and a 24 hour clock:
12 hour format       24 hour format
12 A.M. 00:00 hours
1 A.M. 01:00 hours
2 A.M. 02:00 hours
3 A.M. 03:00 hours
4 A.M. 04:00 hours
5 A.M. 05:00 hours
6 A.M. 06:00 hours
7 A.M. 07:00 hours
8 A.M. 08:00 hours
9 A.M. 09:00 hours
10 A.M. 10:00 hours
11 A.M. 11:00 hours
 
Now, the given table shows the different formats of time (in P.M.) represented by a 12 hour clock and a 24 hour clock:
 
12 hour format 24 hour format
12 P.M. 12:00 hours
1 P.M. 13:00 hours
2 P.M. 14:00 hours
3 P.M. 15:00 hours
4 P.M. 16:00 hours
5 P.M. 17:00 hours
6 P.M. 18:00 hours
7 P.M. 19:00 hours
8 P.M. 20:00 hours
9 P.M. 21:00 hours
10 P.M. 22:00 hours
11 P.M. 23:00 hours
 
It can be observed that from 1 P.M. to 11 P.M., the 24 hour time corresponding to the 12 hour time can be obtained by adding 12 to the hours column.
Conversely, 12 hour time corresponding to 24 hour time for these times can be obtained by subtracting 12 from the hours column.
 
 
Railway time
Observe the following table: …

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