If you haven't done any of the other coin problems, then you might want to go back and try those now, this one is very difficult, even if you have figured out the other ones.

This time, as the title implies, there are 39 coins, and one is fake. You have a balance scale, which can be used 4 times.

How would you find the fake coin?

Well first divide the coins into three piles. First weigh pile one against pile 2, then pile 2 against pile 3. This will tell you whether the coin is lighter or heavier. On top of that you will know which pile contains the fake coin. so know you have 13 coins and two weighings. then divide the 13 coin group, into 3 groups 4, 4 and 5. then weigh the 4 against the other 4. t worst you're left with the group of 5. Now heres where I'm stuck. you can divide it into 2 groups of 2 and a single coin. Any other thoughts?

Posted by Alan on 2003-04-26 07:18:01