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Flush Draw Probability, CRCarson, 29. Nov 2003 03:52
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My starting hand is suited. Say, Ad9d.

What is the probability of making a flush with five cards to come, AND what is the mathematical formula for calculating it?

Thanks.
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Re: Flush Draw Probability, MozMan, 29. Nov 2003 04:03
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There are 11 cards out of 50 that are diamonds, so you are 50:11, or roughly a 5:1 dog to make your flush.

-Moz

"Hey! You made me ink!"
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Re: Flush Draw Probability, ADAM THE EXPERT, 29. Nov 2003 15:36
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MOZMAN, I LIKE YOU, BUT BOY, ARE YOU WAY OFF!!

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Re: Flush Draw Probability, MozMan, 29. Nov 2003 21:24
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Yup, I was thinking of the four flush... ugh... somtimes one fires off automatically without any real thought! :)

-Moz

"Hey! You made me ink!"
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Re: Flush Draw Probability, PairTheBoard, 29. Nov 2003 05:14
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I'll take a stab at it. I think the answer is around 1 in 17 or so. Let's see if that's what I get. A standard formula used in a lot of these problems counts the number of ways you can choose k objects from N without replacement. We can use shorthand notation for this number as
C(N,k). It is calculalted by:

C(N,k) = N*(N-1)*...*(N-k+1)/k!

where k!= k*(k-1)*...*2*1

You can calculate the probabilities of hitting exactly 3 of your suit, exactly 4 of your suit, and exactly 5 of your suit. Then add them together.

For exactly 3 of your suit, the number of 5 card combinations, not counting order is
C(50,5). This is the denominator. The numerator is the number of ways 3 of your suit can be chosen from 11, multiplied by the number of ways 2 cards not of your suit can be chosen from 39. Thus the probabilty is:

C(11,3)*C(39,2) / C(50,5) =

(11*10*9/3*2)*(39*38/2) / (50*49*48*47*46 /5*4*3*2)

I think I'll just let you punch these into your calculator.

Similarly, the probabiities for exactly 4 and exactly 5 of your suit is given by:

C(11,4) * 39 / C(50,5)

and

C(11,5) / C(50,5)

Calculate all three and add them together.
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Re: Flush Draw Probability, ADAM THE EXPERT, 29. Nov 2003 15:35
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DEAR CRCARSON

ASSUMING THAT YOU NEVER GO FOR A BACKDOOR FLUSH DRAW

THE CHANCES OF MAKING A FLUSH, IS 4.61 PERCENT.

HOWEVER, YOU CANNOT ASSUME THAT YOU WILL NEVER

GO FOR A BACKDOOR FLUSH!! SOMETIMES, THE POT WILL

BE SO BIG, THAT YOU HAVE TO "TAKE ONE OFF" OTHER

TIMES, YOU WILL BE GIVEN A FREE CARD, AND NOW

PICK UP A FLUSH DRAW (AND HAVE SUITABLE POT ODDS

TO CALL)

WITH THESE VARIABLES, IT'S IMPOSSIBLE TO TELL YOU

THE EXACT ODDS, EVEN IF I WAS A MATH GENIUS LIKE

MIKE OR MASON (WHICH ALL MY READERS KNOW: I'M NOT!!!

AND NOT ASHAMED OF IT!!)


FIGURE ANOTHER 1 PERCENT OR SO, DEPENDING ON

THE GAME, HOW MANY FREE CARDS ARE GIVEN, POT

SIZE, ET CETERA




ENJOY!!



A.T.E.
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Re: Flush Draw Probability, jajo, 10. Dec 2003 09:08
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The easiest and most accurate way to calculate this is by using the combination formula.

all possible 5-card combinations are:
50 C 5 = 2,118,760

combinations that contain three-flush:
(11 C 3) * (39 C 2) = 165 * 741 = 122,265

cobinations that contain four-flush:
(11 C 4) * (39 C 1) = 330 * 39 = 12,870

combinations that contain five-flush:
11 C 5 = 462

adding it all up: 122,265 + 12,870 + 462 = 135,597

135,597 / 2,118,760 = .0639

your chance of hitting a flush is therefore 6 percent.

you can see mnay other odds calculations on my website: http://pokerstrategy.org/poker_stats/poker_stats.htm
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