Multiple choice general knowledge math & puzzles

The average age of a family of 5 members is 20 years. If the age of the youngest member be 10 years then what was the average age of the family at the time of the birth of the youngest member?

  1. 13.5

  2. 14

  3. 12.5

  4. 15

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

Total age = 5 × 20 = 100 years. Age of 4 members when youngest was born = 100 - 10 - (4×10) = 50 years. Average = 50 ÷ 4 = 12.5 years. We subtract 10 years for each of the 4 older members from the moment 10 years ago.