Mr. and Mrs. Wilson and their children were going to begin their vacation one day, and they had to be at the airport at eleven-forty AM. "It'll take us half an hour to get there in the taxi," Mr. Wilson said, "so we all have to be ready by eleven o'clock. Nobody should be late."

　　At ten minutes to eleven they were still all running around doing things, except Mrs. Wilson, who was sitting quietly on a chair in the garden enjoying the sun.

　　Her husband and children were very surprised that she wasn't in a hurry too, until the taxi arrived and Mrs. Wilson said to them, "Well, I knew that this was going to be happen, so before I went to bed last night, I moved all our clocks and watches ahead twenty minutes. So now we can go to the airport quietly without worring about being late."