A father is three times as old as his son today. In 18 years, he will be twice as old as his son. How old is the son now?

Question: A father is three times as old as his son today. In 18 years, he will be twice as old as his son. How old is the son now?

1. 19 years
2. 17 years
3. 20 years
4. 18 years

Correct Answer: D — 18 years

Explanation: Let son be x and father 3x; after t years solve 3x + t = 2(x + t).
3x + 18 = 2(x + 18), hence x = 18 years.