Four cousins have an average age of 23 years. Three of them are 20, 21 and 24. How old is the fourth?

Question: Four cousins have an average age of 23 years. Three of them are 20, 21 and 24. How old is the fourth?

1. 28 years
2. 26 years
3. 29 years
4. 27 years

Correct Answer: D — 27 years

Explanation: The combined age is average × four; subtract the three given ages.
Fourth age = 4 × 23 − 20 − 21 − 24 = 27 years.