From a class of 42 boys, a boy aged 10 years goes away and in his place, a new boy is admitted. If on account of this change, the average age of the boys in that class increases by 2 months, the age of the newcomer is :

According to the question,
Due to newcomer average age is increased by = 2 months
Total age increment in 42 boys
= 42 × 2
= 84 months or 7 years
Note : If the age of newcomer is same as the boy which was replaced then there is no effect on 2 months.
∴ Age of new boy
= 10 + 7
= 17 years