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Math & Logic · Ages 18+

Riddle #208

A father is currently 4 times as old as his son. In 20 years, he'll be exactly twice as old as his son. How old are they now?

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Answer: The father is 40 and the son is 10.

f = 4s and f + 20 = 2(s + 20) → 4s + 20 = 2s + 40 → s = 10, f = 40. Check: in 20 years, 60 = 2 × 30.

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