Question

The average age of boys and girls in a class is 10.5 years; that of the boys is 10.6 years and that of the girls is 10.1 years. If there are 60 boys in the class, how many girls are there in the class?

A.
15
B.
20
C.
22
D.
25

Accepted Answer

A. Using Alligation: Boy's avg = 10.6, Girl's avg = 10.1, Total avg = 10.5. Ratio of Boys : Girls = $(10.5 - 10.1) : (10.6 - 10.5) = 0.4 : 0.1 = 4 : 1$. Given Boys = 60 $\Rightarrow 4x = 60 \Rightarrow x = 15$. Number of girls = 15.

Number of Girls in Class

Explanation

Practise this under exam conditions