someone tell me how this works?

Conquer Club, a free online multiplayer variation of a popular world domination board game.
http://146673-www3.conquerclub.com/forum/
http://146673-www3.conquerclub.com/forum/viewtopic.php?f=8&t=3428
Proof
let digit 1 be x
let the second digit be y
the number xy can be written as 10x + y
10x+y - (x + y) = 9x...
9x is a multiple of 9 QED
PaperPlunger wrote:f*ck! I started this post like half an hour ago, then stupid sir gordalot goes and posts while I wasa researching!! argh!