Question

There are 50 boys in a class. One boy weighing 40 kg goes away and at the same time another boy joins the class. If the average weight of the class is thus decreased by 100 g, find the weight of the new boy? 

(a) 32 kg 

(b) 40 kg 

(c) 35 kg 

(d) 37 kg

Answer 1

Answer is: (C) 35 kg.

Let the average weight of the class be x kg. 

Total weight of 50 boys = 50x kg 

If y is weight of the new boy, then 

50x – 40 + y = 50 × (x – 0.1) 

⇒ 50x – 40 + y = 50x – 5 ⇒ y = 35 kg.