Answer : Lateral Thinking – The Elevator Puzzle

Answer to the Lateral Thinking – The Elevator Puzzle 

A man lives on the twelfth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator — or if it was raining that day — he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up two flights of stairs to his apartment.