The average age of 30 boys in a class is 15 years. One boy, aged 20 years left the class, but two new boys came in his place whose age differ by 5 years. If the average age of all boys now in the class became 15 years, the age of the younger newcomer is:

15 years

Let the age of younger boy is y years and the age of older one is (y+5) years.

ATQ,

⇒ (31 × 15) = (30 × 15) - 20 + y + y + 5

⇒ 465 = 450 - 15 + 2y

⇒ 2y = 30

⇒ y = 15