Take the following example.

Three man enter a hotel and ask the clerk for three rooms. They each pay the clerk ten dollars. The clerk gives the money to the manager who saids, "here is five dollars. I want you to give one dollar back to each person and keep two for yourself."

Now for the faulty logic. The clerk gave one dollar back to each person. That means each person paid nine dollars. 9 dollars per person x 3 people equals 27 dollars. Twenty seven dollars plus the two dollars the clerk kept equals 29 dollars. Where did the other dollar go?