Class interval: 25-35 35-45 45-55 55-65 65-75 Frequency: 6 10 8 12 4

Class interval:

25-35

35-45

45-55

55-65

65-75

Frequency:

6

10

8

12

4

Let the assumed mean (A) = 50

Class interval	Mid value	d_i = x_i - 50	u_i =	Frequency (f_i)	f_iu_i
25-35	30	-20	-2	6	-12
35-45	40	-10	-1	10	-10
45-55	50	0	0	8	0
55-65	60	10	1	12	12
65-75	70	20	2	4	8
				N = 40	∑f_iu_i = -2

We have, A = 50

h = 10

Mean = A + h *

= 50 + 10 *

= 50 – 0.5

= 49.5

13