Three guys walk into a hotel and order a room.
The desk clerk charges them thirty dollars.
Each guy pays ten.
Later the clerk remembers a room is twenty five.
He takes five ones out of the cash register and sticks two in his pocket. He goes up to their room and tells them that he slightly overcharged them, and gave each of them a dollar back.
That means each guy paid nine dollars.
nine times three is twenty seven and the two
the clerk stuck in his pocket is twenty nine..
Where is the other dollar?