How many shuffles?
August 21, 2011 6:21 AM Subscribe
How many shuffles to randomize a deck of cards?
posted by bukvich to Sports, Hobbies, & Recreation (10 answers total) 1 user marked this as a favorite
a.) 52 standard playing cards, symmetric (upright = upside down)
b.) 78 tarot, symmetric
c.) 78 tarot, upright distinct from upside down.
I read in Scientific American 15 years ago that case (a.) requires seven careful shuffles, and although the bona fides of the statistics guy that wrote this seemed fine, I subsequently confirmed for myself with some tedious experimentation that seven shuffles were good.
Seven shuffles is not sufficient with a tarot deck. The most trustworthy person I know uses 21 which seems a little overdone. I have not been able to find a statistician published number.
If you know the correct permute / combination formula to apply I would appreciate that also.