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dunowhut
Old 01-11-2008, 12:36 AM     Post subject: probability question #1 (permalink)  

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dunowhut
Hi,

i was just wondering how to calculated probability for all 5 cards before u even see it. For example, if im holding any random two cards..say Qh4d..what are the odds i will hit 2 pairs or a set on the flop? can someone show me the calculation method?

tq
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swiggidy
Old 01-11-2008, 01:00 AM #2 (permalink)  
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 I count.

In excel what you need is combin().

There are 3 cards on the flop out of 50, so
=combin(50, 3)
19600

Now count the number of good flops.

2 pair
one Q out of 3 possible Qs
one 4 out of 3 possible 4s
one random out of 44 other cards

=combin(3,1)*combin(3,1)*combin(44,1)
396

trips
pick 2 Q out of 3 Qs
pick 1 card out of remaining 47
=combin(3,2)*combin(47,1)
141

but it could also be trip 4s so multiply by 2
282

Calculate probability
396/19600 = 2.0%
100/19600 = 1.4%
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dunowhut
Old 01-11-2008, 11:36 AM #3 (permalink)  

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dunowhut
http://trackmyhands.com/poker-odds-c...=4&card2suit=h

according to this website the probability of flopping two pair with Q4 on the flop is 4.04%

do anyone knows how to calculate this manually?
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jyms
Old 01-11-2008, 05:12 PM #4 (permalink)  
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 Maybe it would be better if you explained why you want to do this. These are some complicated mathematical calculations that you can't do at the table, if that is what you are thinking.
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swiggidy
Old 01-11-2008, 06:26 PM #5 (permalink)  
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 I ignored cases where the flop is Q22, or 4JJ. Yeah you have 2 pair, but that doesn't mean your hand is any good which is why straight probabilities aren't useful.

I outlined exactly how to calculate manually. You have to think about the different ways to make a hand and count them up.

If you're math minded there is interesting stuff here:
http://www.math.sfu.ca/~alspach/computations.html
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GatorJH
Old 01-12-2008, 01:25 AM #6 (permalink)  
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Quote:
Originally Posted by swiggidy
I count.

In excel what you need is combin().

There are 3 cards on the flop out of 50, so
=combin(50, 3)
19600

Now count the number of good flops.

2 pair
one Q out of 3 possible Qs
one 4 out of 3 possible 4s
one random out of 44 other cards

=combin(3,1)*combin(3,1)*combin(44,1)
396

trips
pick 2 Q out of 3 Qs
pick 1 card out of remaining 47
=combin(3,2)*combin(47,1)
141

but it could also be trip 4s so multiply by 2
282

Calculate probability
396/19600 = 2.0%
100/19600 = 1.4%
My head hurts.
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dunowhut
Old 01-12-2008, 08:30 AM #7 (permalink)  

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Posts: 21
dunowhut
Quote:
Originally Posted by swiggidy
I ignored cases where the flop is Q22, or 4JJ. Yeah you have 2 pair, but that doesn't mean your hand is any good which is why straight probabilities aren't useful.

I outlined exactly how to calculate manually. You have to think about the different ways to make a hand and count them up.

If you're math minded there is interesting stuff here:
http://www.math.sfu.ca/~alspach/computations.html
Ah..i see where the difference comes from now..haha..tq..

btw..do u happen to know how to calculated combine(50,3) manually?? i cant seem to get this right manually..haha..

too trainer_jyms: im just interested in the calculation method..so i can do some calculation at home for fun too see the numbers. Better than just taking it from the internet not knowing it is real or not..lolx
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swiggidy
Old 01-12-2008, 02:32 PM #8 (permalink)  
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 combin(x, y)

x!
y!*(x-y)!
^^ division

Where
z! is a factorial
(z)*(z-1)*...*2*1

so 5! = 5*4*3*2*1

Sample:
combin(50,3)

50!
3!*47!

simplifies to

50* 49* 48
3*2

117600
6

19600
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