Let us find the mean of the following data by step deviation method.

To find mean using step-deviation method, we need to create a table showing frequencies, midpoints and deviations.

Observe that class size, h = (14 – 0) = (28 – 14) = … = (70 – 56) = 14

We have,

A = 35

∑f_iu_i = 8

∑f_i = 90

h = 14

By step deviation method, we can give the formula of mean as:

Using the above values, we have

⇒

⇒

⇒

⇒ Mean = 36.24

Thus, mean is 36.24.