The average age of the 6 brothers is 15 years. The age of the youngest brother is 5 years. What was the average age (in years) of the group of 6 brothers at the time of birth of the youngest brother?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 12.
Present total age of 6 brothers = 6 × 15 = 90
5 years ago, each of the 5 elder brothers was 5 years younger
⇒ Total reduction = 5 × 5 = 25
⇒ Total age then = 90 − 25 = 65
But the youngest was just born → age = 0
⇒ Total = 65 − 5 = 60
Average = = 12