Math behind Winning Perecntages for two hands (or n hands)

[xml2k]

I can calculate the odds of drawing a particular hand, and I like to do math.

Is there a reference to the method of calculating the winning percentages (as is done on the cardplayer.com website) between two hands, or more general theory.

I know the calculator on the website is handy, but I like math and like to know the method behind the numbers.

Best Regards