very clever !!
not mine but thought I should share it
It’s not coming up for me, but is it a card game where it inexplicably keeps picking your card?
The second set of cards are entirely different than the first set of cards.
What the heck? 
I know there’s some sort of code explanation but in the mean time… 
And annoying because it’s been right every time. 
Cool, but easily explained. the formula gives a multiple of nine, every time. The chart changes each time you click the “Try again” button. the symbol shown is simply the one that is next to all the multiples of nine.
say you choose a number with digits “nm”
(10n+m)-(n+m) =
10n +m -n -m =
10n - n = 9n
But clever anyway.
Oh hells.
Math.
I knew I wouldn’t get it.
I know it’s probably as simple as 2+2 for the rest of you, but I did much better at Geometry than Algebra in school.
I’ll stick to “It’s Maaagic!” 
harmless, just take a look at the symbol at 9, 18, 27, 36, 45, 56, 63, 72, 81 and 99. They’re all the same. Click “try again,” and they’re all the same (but a different symbol).
Ooooohh. I see.
Thank you for clarifying that.
Math throws me for a loop.
I’m not dumb (IMHO, of course )…just can’t wrap my brain around some math problems.
Still very cool.
Not to be too picky, you obviously understand the trick, but 99 is not the same. There is no two digit number that you can use to get 99 as your final result.