Clay's method is best explained on paper. Suffice it to say you multiply the digits on the right, cross-multiply and add the digits in the center, then multiply the digits on the left.
Not a particularly novel concept to me. You will still need a highly nimble [read: regularly exercised] memory to accomplish the calculation in your head, and alas, there's no silver bullet magic trick in that, just regular practice.
Darnit! I would have been willing to pay the $33 just to be able to show off, too, but I'm not parting with the cash if his 'trick' means I also have to give up my well-earned trademarked mental laziness.
AD! Pick up the White Courtesy phone, please.
I don’t know. You can probably describe it algebraically. The key to schemes like this is more about utilizing the capacity of human memory than any particular trick.
It’s kind of sad because it isn’t worth $33 these days. I bought a free iPhone app that’s even faster.