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 the number of boys and girls in the class are respectively : 

(a) 72, 64 

(b) 38, 64 

(c) 72, 48 

(d) 62, 58

Answer 1

Answer is: (c) 48

Let the number of boys be x. Then, 

The number of girls = (120 – x) 

Total weight of 120 students in the class = 120 × 56 kg = 6720 kg 

Total weight of x boys = 60x kg 

Total weight of (120 – x) girls = (120 – x) × 50 kg = 6000 – 50x 

Given, 60x + 6000 – 50x = 6720

⇒ 10x = 720 ⇒ x = 72 

∴ Number of boys= 72, 

Number of girls = 120 – 72 = 48