Using step-deviation method, find mean for the following frequency distribution

In the given table i is the class interval which is equal to 15.

Class	Class mark (x)	d = (x - A)	u = d/i	Frequency (f)	fu
0-15	7.5	-45	-3	3	-9
15-30	22.5	-30	-2	4	-8
30-45	37.5	-15	-1	7	-7
45-60	A = 52.5	0	0	6	0
60-75	67.5	15	1	8	8
75-90	82.5	30	2	2	4
Total				Σf = 30	Σfu = -12

Mean = A + $\frac{Σfu}{Σf} \times i = 52.5 + \frac{-12}{30} \times 15$

= $52.5 - \frac{180}{30}$

= 52.5 - 6

= 46.50

Hence, mean = 46.50