http://www.milaadesign.com/wizardy.html

 

that is soooooo old.... and deceptively simple... btw, those symbols always change and the answer will always be correct.

 

go ahead and elaborate a little more on why it's so simple because i still don't get how they do it

 

when you choose a number say 38. You take 3+8 and that's 11. 38-11= 27. No matter what 2 digit number you choose, it will always be divisible by 9. If you notice the chart they show, it always change, but all of the 9's and all of the numbers divisible by 9 are the same. Try it.

Another number... 89. 8+9=17. 89-17=72
Another number... 49. 4+9=13. 49-13=36
And so on.

 

I learned a couple of those tricks in Highschool. Pretty cool stuff (to me), you can also apply some to playing cards and do some pretty amazing card tricks.