There are three men staying in a motel, and they give the guy behind the desk at the motel 10 dollars each to order them some pizza.
When the pizza is delivered, the bill is only 25 dollars.
Because he can’t be bothered fnding change, the guy behind the desk gives them one dollar back each, and pockets the remaining two dollars himself.
Each of the guys has now paid 9 dollars ( having given him 10 dollars in the first place, and getting 1 back with their pizza ), which comes to 27 dollars. The guy behind the desk has the 2 dollars that he pocketed. The 27 dollars paid by the three men and the 2 dollars he pocketed come to a total of 29 dollars.
Where is the other dollar from the original 30 ?