Here’s something fun to try. Sorry if this has already been done on this board. NO - no ghosts pop out!
Yeah, we’ve all seen it. 
[sub]Don’t feel bad, about 20 other people posted that in GQ asking how it worked this past month[/sub]
I figured it might have been here already. Thats why I apologized in advance.
Is cool. Here’s your test: Do you know how it works? 
It’s a mathematical equation that works for every 2-digit number. The numbers equal multiples of 9.
10-(1+0)=9
11-(1+1)=9
17-(1+7)=9
25-(2+5)=18
27-(2+7)=18
35-(3+5)=27
37-(3+7)=27
45-(4+5)=36
47-(4+7)=36
57-(5+7)=45
78-(7+8)=63
83-(8+3)=72
The symbol itself changes everytime you do it, but the same symbol is always used for all multiples of 9. That about right?
You pass. slaps a gold star on your forehead
I hadn’t seen this before and I’m ashamed to admit I was seriously spooked until I searched the web for an explanation.
I figured it out on my own! And considering how math challenged I am, this is an accomplishment.