I'm not sure you'll find this convincing, but this is simply a matter of adding up the wrong elements. First, the business of there being 3 men, and the manager changing his mind, are just red herrings. Even if there was one guest, and he gave the manager �30 for a �25 room, and then gave the bellboy �2 of his �5 change, you might still think he'd paid �27 for the room (�30 less the �3 in his hand), given �2 to the bellboy, and wonder where the thirtieth pound had gone - but you would be making the same mistake. After all, suppose he gave the whole �5 change to the bellboy, would you then say he'd paid �30 for the room, and given �5 to the bellboy, making �35; so �5 had come out of thin air? The correct equation is that at the end of the transaction the manager has �25, the guest(s) �3, and the bellboy �2; making �30 in all.