Multiple choice

The average age of a family of 8 members is 22 years. If the age of the youngest member be 8 years, the average age of the family at the birth of the youngest member was?

  1. 18 years

  2. 16 years

  3. 23 years

  4. 22 years

  5. None of these

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

Current total age of 8 members = 8 × 22 = 176 years. At the birth of the youngest (8 years ago), each of the other 7 members was 8 years younger. Their ages 8 years ago totaled 176 - 8 - (7 × 8) = 176 - 8 - 56 = 112 years. Average age at that time = 112/7 = 16 years. The key insight: subtract 8 years from each of the 7 existing members' ages, then calculate the average.