First, suppose we number all the cards in a deck consecutively from the top, 1-52. With some reflection, one might ask, what does it even mean to say that the cards are now in a random order? Isn’t every order a random order? The whole question of randomness is non-trivial, but a quick and dirty explanation as applied to shuffling depends on two notions. But even with imperfect shuffling, the cards should be fully randomized after seven riffle shuffles. There is no requirement that the cards be perfectly interlaced, nor that the deck be cut into two even packets at the beginning. Most bridge players are familiar with this kind of shuffle.ĭo the cards have to be perfectly alternated, one card from each hand, in perfect syncopation (magicians call this a “faro shuffle”)? Again, the answer is no. This is repeated, riffling off cards from the bottom of the two packets onto the table, alternately, until both packets are exhausted (or at least a little bit sleepy). Then some cards are riffled off the bottom of one packet by the thumb onto the table, and next, some cards are riffled off the bottom of the other packet by the other thumb onto the table. Spoiler: As the host later told the audience, the question’s finish was, “how many riffle shuffles does it take to fully shuffle a deck into a randomized state?” It’s a more interesting question than might appear at first glance, with quite a few sticky points.įirst of all, is it referring to any kind of shuffle? No it applies specifically to the riffle shuffle, also known as the dovetail shuffle-the deck is divided into two packets, one packet held from above in each hand, with each thumb at one short end of the cards, and the other fingers at the opposite short end. Host: (Stunned silence, then laughter) “Yes, correct.” Host: “According to mathematicians at Harvard and Columbia, how many-”ĭelGaudio (and magicians across the country): “Seven!” What an incredible stroke of fortuitous luck engineered by the quiz show Gods! (not)Īnyway, Derek answered questions like, “Which suit used to be represented by batons and sticks?” and “One of the four Kings’ faces is different from the other three: which, and why?” Of course Derek answered these questions correctly-he is after all performing card magic nightly in his new one man Off-Broadway show, In & Of Itself-but it was the final question that was the most amusing. Yesterday, card magician Derek DelGaudio appeared on NPR radio’s quiz show, Ask Me Another, where his quiz category was…playing cards.
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