what is the differance between between
direct mean method
assumed mean method
and step deviation method.
Because i can't understand where to use which method ?
Please HELP
The following frequency distribution showing the marks obtained by 50 students in statistics at a certain college. Find the arithmetic mean using (1) Direct Method (2) ShortCut Method (3) StepDeviation.
Marks  
Frequency 
Solution:
 Direct Method  ShortCut  StepDeviation  
Marks 
 
Total 



Here x is the middle value of the marks as 20+29 divided by 2 = 24.5
Similarly we have got the values of x
Direct method is the method which will give an approx. value and in this we find the summation of the multiplication of frequency with the middle value (x) divided by the summation of frequency .
Mean = = = 54.9
Assumed mean method : in this method , firstly we get middle value i.e. x and then we assume a number i.e. A from the values of x , then we get D = xA and then we find summation of the multiplication of deviated mean with the frequency
Then we use the formula
Mean = A +
= 54.5 +
= 54.9
Step deviation mean : in this method , we get the value of u by dividing the deviated value(d) by the class interval(i.e.34.5  24,5 = 10) , then we find summation of multiplication of frequency and u
Then we use the formula
Mean = A + *h
= 54.5 +
= 54.9