This one is a classic, and is a great one for the kids at home. It does not involve arms in boxes, suicide, or guns. ;) Many can get this through simple reasoning, and is sometimes solved rather quickly.
As always, if you know the answer from playing this before, please let others play out the game.
Please ask single, yes or no questions. You need to come up with the explanation that tells the story as to why the circumstances happen the way they do.
Every day, a man living on the 40th floor, leaves to go to work by using the elevator. When he leaves, he goes all the way to the first floor, then departs the building. But upon arriving back home, he enters the elevator, goes to the twentieth floor, gets out, and takes the stairs for the last twenty floors. Why?