Fewer Shuffles Suffice

An anonymous reader writes "You may have heard that it takes about seven shuffles to mix up a deck of cards to near randomness. Turns out, though, that most of the time, perfect randomness is more than you need. In blackjack, for example, you don't care about suits. The same mathematician who developed the original result now says that for many games, four shuffles is enough. And the result isn't only important for card sharks. It helps reveal the math underlying Markov Chain Monte Carlo simulations, telling applied mathematicians when they can stop their simulations."

Re:4 shuffles...

[Sun.Jedi]

3, if the dealer is clumsy or awkward.

Unlike blackjack, many of the poker variants pay better the more hands you can 'play'. Slow shufflers ruin my hand/hour numbers, and subsequently my $/hour.

Re:How is this random?

[tomhudson]

That's why, between every interleave, you do a few over-the-hand shuffles.

Re:How is this random?

[Anonymous Coward]

I thought about spending several paragraphs and a couple of examples explaining this, but from past experience I have learned that probability is sometimes counter-intuitive and some people just never get it.

Re:How is this random?

[Anonymous Coward]

Feel free to read the paper [stanford.edu]. After all, this story is about a science paper. How a "shuffle" works is defined in the abstract. It's pretty silly to criticize a paper without even reading it.

Re:How is this random?

[larry bagina]

There's a subtle point that isn't obvious -- the revealed door is never the winning door.

You have a 2/3 chance of guessing wrong. But in that case, the other wrong door will be revealed, so swapping means you win.

Meanwhile, you have a 1/3 chance of guessing correctly, and therefore not swapping only gives you a 1/3 chance of winning.

Re:4 shuffles...

[Sun.Jedi]

I just find it kind of ironic that people are willing to gamble with a random deck of cards, yet unwilling to overlook the smallest risk of a rigged deck.

Since you discuss the online vs brick/mortar differences. Your final comment is even more profound, imho.

I just find it kind of ironic that people are willing to gamble with a random deck of cards, yet unwilling to overlook the smallest risk of a rigged deck.

I think its far more likely for an online deck in poker or multi-deck blackjack to be more (dare I say truly?) randomized than a manual shuffle based on super fast CPU crunched RNG's.

At the end of the day, the number of hands are finite, but it's a really big number for a single 52 card deck.

I found that in Hold'em, there are 1326 possible starting hands and in Stud, 2,598,960 possible.
Source1 [top15poker.com].
Source2 [wikipedia.org].