Help how does it work ?

Gilly said:
It doesn't. It got mine wrong.

[edit]Gave it another go. Still got it wrong.
How did it get yours wrong? It is all fixed, as long as you picked a two digit number is should be correct.

sfx
 
if the number is ab, or 10a+b, then if you subtract (a+b), you get 9a, so the answer will always be amultiple of 9....
 
Choose your two digit number. Let's call the number AB. A is the number of tens, B the number of units.

So your number is:
10A + B

Add the two digits together:
A + B

Take this away from your original number:
(10A + B) - (A + B)
10A + B - A - B
9A

The number you are left with will always be a multiple of 9, and will always be less than or equal to 9*9, as the highest two digit number you can begin with is 99. If you look, all the numbers that are less than or equal to 81 and divisible by 9 have the same symbol.

EDIT: Visage beat me by like a zillion posts.
 
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