I wrote about a brain teaser I encountered as a kid and challenged you to figure out if it has a solution, and if so, what that solution is.

That brain teaser works like this:

You have 12 identical coins. One of them is counterfeit. The counterfeit coin may be heavier or lighter than the others. Using a simple balance scale, and in just 3 weighings, identify the counterfeit coin, and determine whether it is lighter or heavier than the others.

It’s a tricky problem, and I remember being stumped for a long time when I first encountered it as a kid. But it can be solved.

There are twenty-four possible cases. Our solution must uniquely identify each possible case.

Here is the solution.

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