Question

The average weight of 120 students in the second year class of college is 56 kg. If the average weight of boys and that of girls in the class are 60 kg and 50 kg respectively, then number of boys and girls
in the class are respectively :

• A. 72 , 64
• B. 38 , 64
• C. 72, 48
• D. 62 , 58

Answer 1

The correct option is C 72, 48

Let the number of boys be x. Then,
The number of girls = (120 - x)
Total weight of 120 students in the class = 120 x 56 kg = 6720 kg
Total weight of x boys = 60x kg
Total weight of (120 - x) girls = (120 - x) x 50 kg = 6000 - 50x
Given, 60x + 6000 - 50x = 6720
$\Rightarrow$ 10x = 720
$\Rightarrow$ x = 72
$\therefore$ Number of boys = 72,
Number of girls = 120 - 72 = 48