(Q11). The following distribution shows the daily pocket allowance of children of a locality. The mean pocket allowance is Rs. 18. Find the missing frequency f.

Daily pocket allowance (in Rupees ) 11-13 13-15 15-17 17-19 19-21 21-23 23-25
Number of Children 7 6 9 13 f 5 4

Solution:

Daily pocket allowance (Rupees) (C.I.) Number of children (fi) Class Marks (xi) fixi
11-13 7 12
13-15 6 14
15-17 9 16
17-19 13 18
19-21 f 20 f
21-23 5 22
23-25 4 24
- ∑fi = 44 + f - ∑fixi = + f
∴ x̄ =
∑fixi
∑fi

xi = 18 (given)

18 =
+ f
44 + f

18 (44 + f) = + f

20f - 18f = 792-

2f =

∴ f = .