Back in March, I mentioned the Pi Day Magic Trick, brought to you by Brian Brushwood and James Grime. Finally the secret has been revealed!

OK, I've actually discussed the principle of this effect before, including in my Magic of 9 post and my age-guessing post.

However, Brian himself has finally discusses the exact nature of the secret in the video below, and afterwards talks to James Grime about this routine briefly:



I think it's interesting that James Grime was able to use this principle to fool several well-posted math professors. It just goes to show you the power of a simple principle when it's properly disguised.

Another way to disguise the principle is by using subtraction instead of multiplication. Check out 7-up's version of the same effect with Fido Dido, and see if you can discern how the same principle applies here.

Since he mentions that you can still experience this effect on Twitter, this seems like a good time to mention that you can now follow Grey Matters on Twitter at: http://twitter.com/grey_matter