it takes practice to perfect shuffling a deck of cards in a fast and flashy way but a mathematician has pointed out that card aerobatics do not guarantee a random and well shuffled pack peri diaconis compared different shuffling techniques and it seems that the 'riffle shuffle', which involves cutting a deck in half and shuffling the halves into each other, is the most time effective   if done well scroll down for video  peri diaconis compared different shuffling techniques and said the 'riffle' shuffle (pictured), which involves cutting a deck in half and shuffling the halves into each other, is the most effective and random if done well  in a numberphile youtube video, the stanford university mathematician said that if a dealer uses a riffle shuffle, they only need to repeat the process seven times to get a good mix if they are well adept at the card manoeuvre, this could take less than 30 seconds but if they use a flashier overhand shuffle, which involves quickly inserting random chunks of cards from one hand into the majority of the deck of cards held in the other, they will need to do it 10,000 times to achieve similar results this could still be fast in the hands of experts, but still slower than the riffle method ‘there's a third way of mixing cards   used in poker tournaments and monte carlo   i call that smooshing,’ dr diaconis said in a video for numberphile, dr diaconis compared shuffling styles to explain their efficiency (illustrated) if a dealer uses an overhand shuffle (pictured), which involves quickly inserting random chunks of cards from one hand into the majority of the deck of cards held in the other, they will need to do it 10,000 times to achieve similar results to the riffle shuffle  riffle method  technique: cutting a pack of cards in half and quickly shuffling them into each other efficiency: a dealer needs to repeat the process seven times to ransomise the pack and this can be done in less than 30 seconds overhand method  technique: quickly inserting chunks of cards from one hand into the majority of the deck of cards held in the other efficiency: a dealer needs to do this 10,000 times to achieve similar results smooshing method  technique: randomly laying the cards face down on a table and messing them up with the hands over and over again efficiency: one minute of smooshing guarantees a random pack of cards simple method  what: taking one card from the top of a deck and inserting it at random efficiency: it takes 200 or so 'pokes' to randomise a deck, making progress slow the method, which is also known as wash, corgi and chemmy, involves randomly laying the cards face down on a table and messing them up with the hands over and over again it is used in professional poker tournaments the method looks random and is – if it is done for a long enough period time ‘if you smoosh for a minute it passes every test we've ever thrown at it ‘if you smoosh for 30 seconds, it seems ok, but less than that it starts failing tests and someone could make money against you or guess cards,' dr diaconis said this means that while the method is thorough, if done for a minute, it too is slower than the riffle method a technique called smooshing (pictured) also known as wash, corgi and chemmy, involves randomly laying the cards face down on a table and messing them up with the hands over and over again it needs to be done for around one minute for the cards to be truly random and difficult to guess  dr diaconis explained in the video how mathematicians check that shuffling is random he said that there are a staggering 80,658,175,170,943,878,571,660,636,856,403,766,975,289,505,440,883,277,824,000,000,000,000 configurations in a perfectly random deck ‘it's more than the number of particles in the universe,’ he said one way of defining randomness is that all card configurations should be equally likely he said that if a deck of cards is perfectly shuffled, you may expect to guess between four and five cards correctly as they are pulled out one by one from a pack but if they are not shuffled enough – for example, if a pack is riffle shuffled four times instead of seven   people might guess nine or ten cards correctly in the simplest form of shuffling, where a person takes one card from the top of a deck and inserts it at random, it would take ‘200 or so pokes’ before the deck is random
stanford university peri diaconis
a stanford university mathematician compared  shuffling techniques . dealers using a 'riffle' shuffle need to repeat the process seven times to get a random pack of cards, said peri diaconis . this technique involves cutting a deck and shuffling the halves together . whereas 'overhand' needs to be repeated 10,000 times to get same results . the 'smooshing' or wash method takes one minute to randomise cards 