Multiple choice

The average age of 20 boys in a class is 12 years. 5 new boys are admitted to the class whose average age is 7 years. The average age of the boys in the class becomes

  1. 8.2 years

  2. 9.5 years

  3. 12.5 years

  4. 11 years

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Total age of 20 boys = 20 × 12 = 240 years. Total age of 5 new boys = 5 × 7 = 35 years. Combined total age = 240 + 35 = 275 years for 25 boys. New average = 275 ÷ 25 = 11 years. This is a weighted average problem where the final average depends on both group sizes.