Question

If the mean of the following distribution is 24, find the value of 'a '.

Marks	0-10	10-20	20-30	30-40	40-50
Number of students	7	a	8	10	5

Answer 1

We have,

C.I.	f	Class mark x	fx
0 - 10	7	5	35
10 - 20	a	15	15a
20 - 30	8	25	200
30 - 40	10	35	350
40 - 50	5	45	225
	`sumf = 30 + a`		`sumfx = 810 + 15a`

Mean 24 (given)

`=> (sumfx)/(sumf) = 24 => (810+15a)/(30 + a) = 24 => 810 + 15a = 720 + 24a`

`=> a= 10`