Riddle 6: A Weighty Matter

by William Jackson on 2007-03-30

I like to cook, though I do not do it very often. I also like to bake. I think I would bake more if I had one of those scales and all my recipes measured ingredients in grams. Mass is much more precise — not to mention much more fun — than volume.

You are given eight coins and told that one of them is counterfeit. The counterfeit one is slightly heavier than the other seven. Otherwise, the coins look identical. Using a simple balance scale, can you determine which coin is counterfeit using the scale only twice?