There's only one room left, so they agree to share. The desk clerk charges them thirty dollars, and they each give him ten dollars.

Later, the clerk realizes he's over-charged them by five dollars. He gives the bell-boy five one-dollar bills, and tells him to return the money to the three men. The bell-boy keeps two dollars for himself, and gives one dollar to each of the three men.

So, the men paid nine dollars each for the room, for a total of twenty-seven dollars. The bell-hop has two dollars, and that makes twenty-nine. What happened to the other dollar?