Question

Find the mean of the following frequency distribution:

Class:	10 – 15	15 – 20	20 – 25	25 – 30	30 – 35
Frequency:	4	10	5	6	5

Answer 1

Class	Mid-point `(bbx_i)`	`bb(f_i)`	`bb(d_i = x_i - A)`	`bb(f_i d_i)`
10 – 15	12.5	4	– 10	– 40
15 – 20	17.5	10	– 5	– 50
20 – 25	22.5 = A	5	0	0
25 – 30	27.5	6	5	30
30 – 35	32.5	5	10	50
Total		`sumf_i` = 30		`sumf_i d_i` = – 10

Here, assumed mean, A = 22.5

Mean = `A + (sumf_i d_i)/(sumf_i)`

= `22.5 + (-10)/30`

= 22.5 – 0.33

= 22.17