Besides the announcement of my recently-released Knight's Tour+ App, I've quietly made a free goodie available. I've just posted lessons on solving the 15 puzzle!

To make it easier to understand, I've broken the process down step-by-step, and used jQuery and the jqPuzzle plug-in to provide working 15 puzzles to help you learn at every step.

First, I teach you the technique for working the upper rows, using a 3 by 3 puzzle. Next, still staying with the 3 by 3 puzzle, I teach how to solve the last two rows.

After learning those two techniques, you'll learn how to put those 2 techniques together to tackle the traditional 15 puzzle, as well as larger ones!

Many 15 puzzle lessons would stop there, but I continue on to discuss interesting variations. The first variation is the pictorial 15 puzzles, which can be tricky since they often lack numbers.

Next, with a little help from James Grime, you learn about why some puzzles, such as Sam Loyd's classic 15-14 puzzle, are unsolvable in the traditional manner. However, you'll also learn about puzzles that seem unsolvable, but really can be solved. This includes the 1959 RATE YOUR MIND PAL version depicted above.

To conclude, I teach how to solve the 15 puzzle as a magic square. Since this requires memorizing a particular pattern, I've put the magic square 15 puzzle quiz on an entirely different page.

I first put the magic square 15 puzzle on Grey Matters about 5 years ago. It's nice to have working lessons all in one place to make this easier to understand and learn.

Did you learn from these lesson? Do you have any questions or criticisms about these lessons? I'd love to hear them.