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

???

You alwys end up with a multiple of 9 & all multiples of 9 have the same symbol.

I've just done that three times in a row and it worked every time - all with different symbols at the end.
Realised the first time I hovered my cursor key over the answer so changed it the second and third time and hovered over the wrong answers but it still worked both times.
I'm a bit dense when it comes to these things but thats bugging me, how it got it spot on each time.