Many a family game night has been interrupted by arguments that someone had not shuffled the deck of cards properly, thus giving an unfair advantage.
So just what is "good" shuffling?
Persi Diaconis, a mathematician at Stanford University, appeared on the YouTube channel Numberphile to explain the math behind a properly shuffled deck of cards.
He gets into some technical details involved with card schemes, but here are the takeaways for shuffling methods:
If you're going to shuffle using the "riffling" method — that sorta fancy one with the bridge effect — Diaconis said you need to do it seven times to get a good mix.
The "overhand" shuffle — the kind that looks less complex like you're just dropping a few cards from one hand into the other — would require 10,000 shuffles to be fairly mixed, he said.
Then there's smooshing, where you put all the cards on the table and swirl them around.
"If you smoosh for a minute, it passes all the tests we've ever thrown at it," Diaconis said.
Watch his full explanation:
(H/T: Mental Floss)