Sorry folks, I can’t take the email so I’m going to spill the beans on the psychic timewaster below. Here’s an email from one of the many readers who got it:

Jonah:
While John Vernon trivia may be too tough for my readers, this particular puzzle is not. There are only nine unique solutions to the problem (x*10+y) – (x+y) where x is between 1 and 9 inclusive and y is between 0 and 9 inclusive. Those 9 solutions have the same symbol each time you try. It’s clever in the same way the “take your birthday, subtract this, divide that, and your result is…”.

Me: What he left out is the way the site changes the symbols after every turn to throw you off. But if you look the possible answers all have the same symbol. Still, use it on your friends.