Magic squares? Mind-reading? High school maths, and nothing more.

I've come across an interesting site (which was advertised on another site I found through StumbleUpon), featuring a supposedly mind-reading magic square.

This site gets the user to choose a two digit number at random, and then subtract from this number the values of its digits, e.g. if you chose 87, you would then subtract 8 and 7 from 87 to get 72. You then look at a grid showing numbers and symbols, and find the symbol corresponding to your result.

The site tells you it will guess your symbol correctly three times, then if you pay $2 via PayPal, you can get five more guesses and a presentation about the "Secret to Life". And you can pay $20 to have the secret of the magic square explained to you.

Of course, there is no magic, and no mind-reading, and a bit of elementary maths can quickly reveal what's going on. This is actually a good exercise for both Mathematics and Computer Studies classes - construct a spreadsheet or computer program that shows all the numbers from 10 to 99 and the result after subtracting the number's digits from itself. Once you've done that, the trick is obvious.

What about the "Secret to Life"? I didn't pay to find out, but I suspect it might be that a fool and his money are soon parted.