I saw this interesting problem in a Mathematics book in Chinese(I translated it):
You and your friend is playing a game. There is a square swimming pool, and you are in the middle of it. Your friend is at one of the cornercorners of the square pool. Your goal is to escape from your friend, and he must notcannot swim in the pool. His running speed is three times of your swimming speed but you run faster than him. Can you escape from him?