# 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:

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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