Question

The mean weight of 60 students in a class is 60 kg. The Mean weight of boys is 70 kg while that of girls is 55 kg.

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

Answer 1

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
Number of girls = 60 - 20 = 40