This should confuse... You and two other people go to a restaurant. The bill comes to 30 pounds so you decide to split it between you, 10 pound each. The waiter takes the money to the kitchen. He is told he has over charged you by five pounds. On the way to returning the money to you he realises he can make a profit here. He takes two pounds and gives you each a pound back, so you have each only paid 9 pounds each. So three 9's are 27 and the waiter has two pounds, so where has the opthr pound gone?