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

Answer: Option B

Let the age of younger boy = x years
Then the age of older boy = (x + 5)
According to the question,
⇒ (30 × 15) - 20 + x + x + 5 = 31 × 15
⇒ 430 + 2x + 5 = 465
⇒ 2x = 30
⇒ x = 15