Fido Puzzle

[polarpi]

I got this website in an email....and I can't figure out how it works!

Here's the site:

Fido Puzzle

[AOII*Azra-elle]

kinda freaky

[Xylochick216]

We had to do something like that for a math class sometime... it's something about inverse numbers and they all have different answers when you subtract so if you know 3 numbers, you can figure out the fourth... it's fun to watch people get frustrated when the computer can guess their answer. My friend was baffled when I showed this to her

[CatStarESP4]

I did that puzzle twice today and both times he guess my number correctly. This is a very awesome puzzle!