Multiple choice

The average age of a class of 30 students is 15.2 years. If 15 more boys joined the class, the average age of the class is decreased by half year. What is the average age of new boys?

  1. 12.5 years

  2. 14.7 years

  3. 13.5 years

  4. 13.7 years

  5. None of these

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

Original total age = 30 × 15.2 = 456 years. New total = 456 × (15 students) = 6,840. New average = 6,840 ÷ 45 = 14.7 years. Let x be average age of new 15 boys: 456 + 15x = 6,840, so 15x = 6,384, giving x = 425.6 ÷ 15 ≈ 13.7 years.