Question 26602
Hi,

This is quite a famous problem. If you searched the web, you might find a better explanation than mine, but here goes.

1) Split the coins into 3 piles, two piles of six, and one pile of one. Weigh the two piles of six, if they are equal then the heavier coin must be the other one and you're done. If they're not equal then the heavier pile contains the coin.

2) Take the pile of six coins that contain the heavier one, and split it into three piles of two. Weigh two of these piles. If they are the same then the heavier coin is in the third pile, else it is in the heavier pile.

3) You should now know that the heavier coin is one of possibly two. Weigh them and the heaviest is your coin.

Hope that helps,
Kev