#1
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Probability of 4 to a straight or a completed straight on the board
Hi
Can someone tell me what the probability of this is after the river card in holdem? e.g A23x5, 89TJx, 45678, 9xJQK Thanks Bilko |
#2
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Re: Probability of 4 to a straight or a completed straight on the board
There are C(52,5) = 2598960 combinations of board cards that
are possible. Some might recall these common numbers from draw poker: 40 straight flushes 10200 straights Now it remains to calculate four-card straights. There are basically two types, four in a sequence and those with one gap inside (gutshot). Of the first type, the sequences with an ace do allow an extra rank which won't produce a five card straight on board. There are 11 sequences and 10x3=30 one-gappers. The following include 5 card flushes on board; if you want to exclude those, take away 4 of the 1024 suit combinations allowed for the nonpaired boards below. No pair: 2x(8x1024) + 9x(7x1024) + 30x(8x1024) = 319 x 1024 = 326656 (five card flushes: 319 x 4 = 1276 so those without a five card flush on board 325380) Pair: (11+30)x4x6x64 = 62976 Summing, 10200+325380+62976 = 398556. Altogether, excluding five-card flushes on board, there are then 398556 possibilities yielding a probability of about 0.1533521. This explains why when playing draw poker everyone seems to notice getting a lot of straight draws, especially gutshots! Now, if you include five-card flushes (don't know exactly why you would), there would be an additonal 40+1276 = 1316 hands making the total now 399872 hands and the probability 0.1538585. |
#3
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Thanks... (N/T)
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