Mystery

Here’s a little puzzle. In the physical version, there are six cards with numbers printed on them. I’ve reproduced them here and labeled them A–F for convenience.

 

Here’s how the game goes. You choose any number on any one of the cards—it doesn’t matter which, just so long its on at least one card. Once you’ve chosen your number, keep it secret, and then tell your friend or classmate which cards on which it appears.

So for example, say I chose 42. Then I’d tell my friend that my card appears on cards B, D, and F. Then it’s my friend’s job to guess my number.

Of course, there’s a trick to this—and it doesn’t involve having to scan or compare cards, hunting for numbers. There’s a quick calculation you can perform.

Try it out and see if you can determine the quickest, infallible way to guess the secret number.

Copyright © 2025 Clayton Cafiero

No generative AI was used in producing this material. This was written the old-fashioned way.