Q. 95.0( 3 Votes )

The table below gives the percentage of girls in higher secondary science stream of rural areas of various states of India. Find the mean percentage of girls by step-deviation method:


Answer :

This is a grouped frequency distribution.


In step deviation, we need to mark the assumed mean in xi. Step deviation also calculates deviation of each xi values from the assumed mean using a formula.


The assumed mean is the value from xi closest to the central value.


So, assumed mean is


A = 50


Here, class interval is given by


h = 10 ( 25 – 15 = 35 – 25 = … = 85 – 75 = 10)


We need to represent it in tabular form:



So now, we have


fiui = -29 and fi = 35.


Also, assumed mean, A = 50 and class interval, h = 10.


Mean by step-deviation is given by



[using the values from the table]



Mean = 50 – 8.29


Mean = 41.71


Thus, mean is 41.71.


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