There are four keys of different colors: red, yellow, green, and blue. Each key opens a different box: red, yellow, green, and blue. Here are some clues.

1. No key opens a box of the same color.
2. The red key does not open the yellow box.
3. The green key opens the blue box.

Which key opens which box?

By 3, we know the green key opens the blue box.  Consider the red key. By 1, it does not open the red box. By 2, it does not open the yellow box. By 3, it does not open the blue box. Therefore, the red key opens the green box. The yellow key can't open the yellow box, per 1, and the blue and green boxes are already spoken for. So the yellow key opens the red box. The blue key, then, opens the yellow box.

Posted by Dustin on 2014-08-23 23:11:05