Three men check into a hotel room. The clerk says the room costs 30 dollars. Each man pays 10 dollars. Later, the clerk realizes the room only costs 25 dollars and sends a bellboy with 5 dollars change. The bellboy pockets 2 dollars and gives each man 1 dollar back. So each man paid 9 dollars — 9 x 3 = 27, plus the bellboy's 2 = 29. Where is the missing dollar?