I normally dislike the  imagine-any-number-add-this-minus-this-blah-blah kind of games but today I came across a riddle that will blow your mind.  ( At least until you come to know the secret ). The riddle can be found at

http://www.regiftable.com/regiftingrobinpopup.html.

I know now how it works but if you manage to figure it out, do tell us and we will feature your name in our upcoming  Hall of Fame.