-
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 ages differ by 5 years. If the average age of all the boys now in the class still remains 15 years, the age of the younger newcomer is :
-
- 20 years
- 15 years
- 10 years
- 8 years
- 20 years
Correct Option: B
Let the age of younger boy be y years.
∴ Age of older boy = (y + 5) years.
The average age of 30 boys in a class = 15 years
Then, total age of 30 boys = 30 × 15 = 450 years.
Total age of 31 boys after two newcomers join & 1 left = 450 – 20 + y + y + 5 = 435 + 2y
Clearly, 435 + 2y = 31 × 15
⇒ 2y = 465 – 435
⇒ y = 30 ÷ 2 = 15 years
