Question

The mean weight of 70 Students in a class is 60 kgs. The mean weight of boys is 70 kgs while that of girls is 50 kgs.

Find the number of boys in the class.

• A. 40
• B. 30
• C. 35
• D. 38

Answer 1

The correct option is C

35

Let the number of boys in the class be x.

Number of girls = 70 - x

Mean weight of boys = 70

Total weight of boys = 70x

Mean weight of girls = 50

Total weight of girls = 50 $\times$ (70 - x)

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

60 = $\frac{70x+50\times (70-x)}{70}$

$\Rightarrow$ 70x - 50x + 3500 = 70 $\times$ 60 = 4200

$\Rightarrow$ 20x = 4200 - 3500 = 700

$\Rightarrow$ x = $\frac{700}{20}$ = 35

$\therefore$ Number of boys = 35