A man who lived on the top floor of a twenty story building had to go up and down daily for work, and of course, for food and the other necessities. On most days he could only ride the elevator to the fifteenth story, and he would have to walk the rest of the way. When it rained, however, he could ride all the way up to the twentieth story. Why?
The man wasn't tall enough to reach the button for the 20th floor. He could only reach the 15th story button on the elevator. When it rained, he brought his umbrella, and used it to press the 20th story button on the elevator.
Mr. Steve lives in a mansion. He is very rich. He's so rich that he has a maid, a cook, a butler, and a lifeguard. Yesterday, Mr. Steve was found dead. The chief detective was coming from Sunday church to investigate. The police were already there. They caught 6 suspects. The maid, the butler, the cook, the lifeguard, the postman, and Mrs. Steve. The maid said she was dusting. The butler said he was playing a board game with Mr. Steve's sons. The cook said he was making dinner. The lifeguard said he was watching Mr. Steve's daughter swim in the pool. The postman said he was delivering mail. Mrs. Steve said she was watching TV. Who is lying? You only have one chance because if you choose incorrectly, you accuse the wrong person and the true killer gets away.
The postman was lying. If the chief detective was coming from church, then you know that the post office doesn't deliver mail on Sunday.