Question

The Mean weight of 60 Students in a class is 60 kgs. The Mean weight of boys is 70 kgs while that of girls is 55 kgs.

Find the number of boys and girls in the class respectively.

• A. 24 and 36
• B. 18 and 42
• C. 25 and 35
• D. 20 and 40

Answer 1

The correct option is D

20 and 40

Let the number of boys in the class be x.

Number of girls = 60 - x

Mean weight of boys = 70

Total weight of boys = 70x

Mean weight of girls = 55

Total weight of girls = 55 $\times$ (60 - x)

Mean = $\frac{Totalweight}{No.ofStudents}$

60 = $\frac{70x+55\times (60-x)}{60}$

$\Rightarrow$ 70x - 55x + 3300 = 60 $\times$ 60 = 3600

$\Rightarrow$ 15x = 3600 - 3300 = 300

$\Rightarrow$ x = $\frac{300}{15}$ = 20

$\therefore$ Number of boys = 20 and number of girls = 60 - 20 = 40