Like mind bogglers?

[Lulav]

Try this one

http://digicc.com/fido/

A friend sent it to me and He is pretty smart but can't figure out how they do It, I think someone could run a computer program and figure out the percentages of combinations one would pick and then select out of three numbers.

I've done it twice and it's spooked me, but I'm sure there is a logical solution....................

[johnd]

beat the system.

Do all the same number.

its a trick nothing more.

[varsity]

After you subtract, the sum of the digits is either 9, 18, or 27. So he simply sums the digits of the number you send and then finds what digit will bring the sum to 9, 18, or 27. It's based on the same principle as "casting out nines".

http://en.wikipedia.org/wiki/Casting_out_nines