PolySciFi Blog

Friday, September 16, 2005


A simple card probability approximation

This may be a rather commonly-known trick - I'm not a big poker player (read as I haven't read any books or played online or played in Vegas) - but I ran it by Thason and he hadn't heard of it either.

Frequently, it's useful to be able to estimate the probability of drawing cards in terms of percentages (for instance, when calculating pot odds). There's 52 cards in the deck and I've always found working in 1/52nds to be rather unwieldy. However, 50 is a pretty good approximation for 52. So rather than doing math in my head using 1/52nds I can use 1/50ths, or 0.02. So if there's 7 cards that will win me hand, then I estimate I've got 7*0.02 = 14% chance of winning.

Now imagine calculating 7/52 in your head. (It's 13.46%)

So this method won't give you the exact probability, but it's pretty close, and I think you'll find it to be quite useful after a few beers. Of course, if you're playing texas hold 'em with 2 hole cards, then the calculation is exact. (It's also not a bad approximation for 46, 47, 48, or 49 cards either.)


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