I always enjoyed this one:
3 men stop at a hotel for the night and each asks for a room. The hotel owner says "that's $10 each". So they each pay their $10 (total $30) and go up to their rooms (this must be an old teaser at these prices!). The owner then feels guilty and tells his bellhop, "hmmm, I charged them a little too much for these rooms. Here, take $5 and give it back to them". As the bellhop walks up the stairs, he's thinking "gee, how am I going to split up $5 among 3 people?". So he pockets $2 and gives each man $1 back.
So now, the men have paid $27 for their rooms (3 times $9) and the bellhop got another $2. Where did the other dollar go ?