The mind reader!

[clarinetJWD]

Hertz just cheated too! Look at the proof if you don't understand. Proof-->When you subtract the number from it, it only gives multiples of 9. THere's only one symbol he could choose...

 

[Unimaxium]

Ah ha... I figured out the fact that the math you did narrowed the possible choices to multiples of 9, but the part I didn't get was that it cycled between different symbols each time. It confused me how it managed to come up with a different one each time yet still got it right. Now it all makes sense

 

[Kent Frost]

The thing is, when you add the two digits of a two-digit number, and then subtract that sum from your original two-digit number, many times you'll come up with a number that is divisible by 3. Easy way to tell: if you can take the 2 digits of your final number and the sum of those two numbers is a number divisible by 3, then it's probably going to get it.
Example:
42. 4+2=6, divisible by 3.
63. 6+3=9, divisible by 3.
246. 2+4+6=12, divisible by 3.

You get the idea.