This is a problem which stumped me for about a minute once I was told it.  Dunno how good you guys are, but let's see if you can figure it out.

3 people decided to share a hotel room for a night, costing $300 in total for the night.  They decided to split the costs evenly, so that's $100 paid each.
After they paid, a while later, a clerk realises that they were overcharged, and that the room really cost only $250 for the night.  The clerk, trying to be a bit sneaky, decides to only refund $30, keeping $20 to himself.
This $30 refund is split evenly amongst the 3 people.
In other words, each effectively paid $90 ($100 - $10), or $270 in total.  Now, since the clerk took $20, the amount paid + "'borrowed'" amount is $290.  But $300 was originally paid.  Where did the extra $10 go?

(This post was last modified: 21/04/2010 05:28 AM by ZiNgA BuRgA.)