Ma Ma Jacquie's Blah Blah Blog

That's so easy. It reads your mind.
 

Yes, I've seen these before. It works by changing the symbols next to the numbers every time.

There are a limited number of possible "answers", and these all get the same symbol drawn next to them every time.

Try this test: pick one (like 99 for example, which would give you 81 as the answer). Watch the symbol for 81, and it will appear when you click it. Then when you "try again" it shuffles up the symbols & numbers, but you will notice that all the *valid* answers (81 and all the others) will have the same symbol, and this will be the one that appears.
 

Oh yeah. Duh. Now, I get it. I kind of figured the mathematical part out but I didn't take into consideration the changing of the symbols.
 

I lost interest when I saw it involved math.