Quote[/b] (herenorthere @ Jan. 14 2005,2:55)]The algebra of it is that your two digit number is 10X + Y. The site's example is 23, so X = 2 and Y = 3. The site tells you to add X + Y and subtract it from 10X + Y. That's 10X + Y - X - Y and that's equal to 9X. So, no matter what two digit number you chose, you'll end up with a multiple of 9. And that table uses the same symbol for 9, 18, 27, and every other whole number multiple of 9, up through 81. Those are the only possible answers if you start with a two digit number.