Ok take a piece of paper and drawl a tic-tac-toe board. Now use this board to do the following.
Useing the numbers 1 - 9 place them on the board so that from every direction, includeing angles, it adds up to 15. You may not use 0 and u may not, at any time, go over 15. Each number may only be used ONCE.
This is possible, some of you may get it very quickly, whereas others may need more time, it took me two class periods, roughly an hour and 45 minutes.