Correct Answer - Option 3 : 3 : 1
Given
The average weight of boys in the class is 50 kg and girls is 70 kg
The average weight of whole class is 55
Concept used
Mixture and alligation concept used
Calculation
Let number of boys be x and girls be y
Total weight of boys = x × 50
Total weight of girls = y × 70
Total student = 55(x + y)
⇒ 50x + 70y = 55x + 55y
⇒ 5x = 15y
⇒ x : y = 3 : 1
∴ The ratio of boys and girls in the class is 3 : 1.
