Saw this problem from slashdot yesterday. It gave me the shits so much I had to look up the answer ;)

Hope somebody else struggles with it too:

Create the number 24 using only these numbers once each: 3, 3, 7, 7. You may use only the following functions: +, -, *, /. This is not a trick question; for example, the answer does not involve a number system other than base 10 and does not allow for decimal points.

Btw this was from

http://www.ocf.berkeley.edu/~wwu/riddles/hard.shtml