As I heard it, the problem goes like this. Three men check into a hotel room, agreeing to share the room rent. The desk clerk says the rent is $30, so they each give $10. Later, the manager tells the desk clerk the correct rent for that room is only $25. He gives the clerk $5 and asks him to return it to the guests. The clerk sees an opportunity to make some money. He goes up to the room, tells the guests the correct rent was $27, and gives each of them $1 back. So now they've paid $27 for the room, and the clerk kept $2, which only adds to $29. Where's the missing dollar?