A class of 48 students has an average score of 65. The boys average 60 and the girls average 72. How many boys are in the class?

Explanation

1. 01

   Boys are 5 below 65 and girls are 7 above it, so boys : girls = $7 : 5$.

2. 02

   Boys = $\frac{7}{12} \times 48 = 28$.

3. 03

   Check: $28 \times 60 + 20 \times 72 = 1{,}680 + 1{,}440 = 3{,}120 = 48 \times 65$.