Question

Find the mean of the following data by step-deviation method :
Classes : 10 – 20 20 - 30 30 - 40 40 – 50 50 - 60
60 – 70
Frequencies : 2 3 5 7 5 3

Answer 1

Solution is in the attachment


STEP DEVIATION :



Step deviation method is  used in the cases where the division from the assumed mean are a multiples of a common number.

If the values of di for each class is a multiple of h ,the calculation become simpler by taking

ui= di/h= (xi -a)/h


Here, h is the class size of each class interval.

The Value of h is equal to the difference between upper and lower class limits of a class.


a = assumed mean


The Arithmetic mean by step deviation method is:


X= a+ ( ∑fi . ui /∑fi ) × h


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Hope this will help you.....

Answer 2

this is your required answer