Three guys check into a hotel room and the desk clerk charges them $30. Each guy pays $10 for the room. The manager tells the desk clerk that the room is only $25 and to give them back their $5. Because the desk clerk is stumped as how to split $5 three ways, he decides to give each guy back $1 and pocket the extra $2.

If each guy gets back $1, then they each paid $9. If 9 x 3 = 27 plus the $2 from the desk clerks pocket, thats $29. Where did the extra dollar go?