A man lives on the 20th floor. Every morning he takes the elevator to the ground floor and goes to work. Every evening he takes the elevator to the 10th floor and walks the rest of the way, unless it is raining. Then he rides all the way to 20.
Why?
Answer
He is too short to reach the higher floor buttons. On rainy days he has an umbrella to press them.
He can reach the lobby button and floor 10. Higher floors need the umbrella tip, or a taller person in the elevator, depending on the version. The umbrella version is the cleanest.
This answer was re-solved from a cold start before the page went live. If you can break it, tell us and we will fix it.
Further reading on lateral puzzles
This one belongs to the situation-puzzle family, where the work is asking the right question rather than doing any arithmetic. Both write-ups cover how that family behaves:
