Sometime last year my kids became fascinated by Rubik’s cubes. Not sure why or how it happened, but once they started playing around a little they were hooked. So much so that learning more about how to solve the cubes seemed like a fun topic to include as part of the school year, so we’ve been studying some of the 2×2 and 3×3 speed solving techniques for fun since September. Even though I’m not practicing the speed solving with the boys, I’ve gotten a little hooked, too 🙂

Following a few folks on twitter also led to some interesting Rubik’s cube related reading in the last year. Christopher D. Long (@octonion) tweeted about the book “Adventures in Group Theory: Rubik’s Cube, Merlin’s Machine & Other Mathematical Toys.” Definitely a fun read if you are into math, though it’ll be a while before I can pull much from it for the boys.

I also ran across Cathy O’Neil’s (@mathbabedotorg) old post about math contests :

Math contests kind of suck

This comment really struck me – “I have never been particularly fast at working out the details of something from the conceptual understanding (for example, it takes me a long time to solve a 7x7x7 Rubik’s cube) but it turns out the Rubik’s cube doesn’t mind. And in fact mathematics in real life isn’t a timed tests- the idea that you need to be original and creative *really quickly* is just a silly, arbitrary way to select for talent.” (as an aside, you should definitely follow her blog and follow her on twitter – you’ll not find a more interesting blog.) I agree with Cathy O’Neil’s point that there’s not anything special about solving the cubes fast. The kids seem to like it and enjoy learning the techniques, but it is mostly just a matter of practice. That said, the world record solve times (~5.5 seconds for solving the 3×3, for example) really are mind blowing.

So, what can kids learn from these cubes?

There is quite a bit of interesting math related to the cube solving algorithms (see the book mentioned above). A simple introduction to these algorithms probably has some benefit, but I’m aiming a little lower right now.

One interesting advanced topic is parity. This position on the 3x3x3 is impossible to solve:

You can not create a position with just one middle reversed with legal moves. In order to make this postion, you have to take the cube apart.

However, this position on the 4x4x4 cube, which seems pretty similar to the picture above, is solvable:

At least for my (very, very very slow) solving technique, figuring out how to solve the 4x4x4 from this position was the final obstacle to overcome in learning how to solve the larger cubes.

For my younger son, it turned out that the cubes were also fun tools for learning about topics like fractions:

ratios:

and exponents:

** Update ** Imaginary and non-commutative numbers!!

It isn’t hard to believe that kids will be more excited about learning when they are having fun, but it great to see that excitement in practice. Of course, it has also been really fun for me to use the Rubik’s cubes to help teach a bunch of different math topics. Maybe one day we’ll even be able to replicate something like this 🙂