What's The Best Way To Shuffle A Deck Of Cards?
How do you shuffle your playing cards? The riffle shuffle may be the most common way, but if you want to truly mix up the deck, you'll need to do it around 7 times. This was proved by Persi Diaconis, a professional magician turned mathematician, in 1992. Diaconis has examined several modes of shuffling in an effort to weed out the inefficient ones and highlight the ones that will lead to fair gameplay. One type of shuffle is especially hard to study, however: the "smoosh," or the technique that involves just laying out all the cards face-down in a mess and swirling them together with your hands. He's found that 1 minute of smooshing typically results in an unpredictable arrangement of cards, whereas 15 seconds isn't long enough. As for all you overhand shufflers out there, bad news: it would take up to 10,000 overhand shuffles to "randomize" a deck as well as 7 riffle shuffles.
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Key Facts In This Video
It takes about 10,000 overhand shuffles to mix up a deck of cards so that their order is unpredictable. (0:43)
There are (52!) possible arrangements of cards in a deck of 52 playing cards, a huge number that is also called "52 shriek." (2:07)
If you riffle shuffle a deck of cards only 5 or 6 times, someone can still make money against you in a card-guessing experiment. (8:32)