Two Plus Two Older Archives odds of flopping quads
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#1
11-11-2002, 11:50 PM
 Guest Posts: n/a

What is the proper formula for figuring the odds
on flopping quads when I have a pocket pair in HE? Any help would be appreciated. I keep getting different answers. Thanks.
#2
11-12-2002, 12:06 AM
 Guest Posts: n/a

You have 2 cards in your hand, leaving 50 unseen cards. There are (50 choose 3)=19600 different flops that can come up. (2 choose 2) * (48 choose 1)=48 of these give you quads. Probability of flopping quads is 48/19600.
Would you believe that once I flopped quads with a pocket pair 4 straight times? Well, you shouldn't.
#3
11-12-2002, 12:13 AM
 Guest Posts: n/a

Thanks for reply. However, I figure the possible flops to be (50*49*48)=117600. I agree on the 48. So, I get 48/117600. Am I miscounting the total number of flop combos?
#4
11-12-2002, 12:24 AM
 Guest Posts: n/a

50*49*48 gives you every possible combination, but it makes it order dependent. Dividing by 6 takes out the order dependency, and gives you the correct total of 19600 combinations.

TT
#5
11-12-2002, 12:26 AM
 Guest Posts: n/a

That's the issue! Thanks to both for the help. Got it now. Much appreciated.
#6
11-14-2002, 03:36 PM
 Guest Posts: n/a

I tried this. Here is my results using Aces.

50*49*48=117600 total possible flops.

AAx = happens 48 times
AxA = happens 48 times
xAA = happens 48 times

144 ways two Aces can come up in 117600 flops.
144/117600 I get 3/2450. [img]/forums/images/icons/confused.gif[/img]

Where does my logic fail? And what does (50 choose 3) and (2 choose 2) and (48 choose 1) mean?
#7
11-14-2002, 06:34 PM
 RocketManJames Senior Member Join Date: Nov 2002 Posts: 118

(N Choose K) is equal to the number of ways that one can choose K differentiable objects from N total differentiable objects (without repetition).

The formula is:

(N Choose K) = N! / [ (N-K)! K! ]

N! = 1 * 2 * 3 * ... * N

Hope that helps!

RMJ
#8
11-14-2002, 07:04 PM
 Guest Posts: n/a

So (48 choose 47) = (48 choose 1) = 48?
but (48 choose 46) = 1028?

I knew I should have studied math.
#9
11-14-2002, 09:08 PM
 Bozeman Senior Member Join Date: Sep 2002 Location: On the road again Posts: 1,213

"AAx = happens 48 times"

"Where does my logic fail? And what does (50 choose 3) and (2 choose 2) and (48 choose 1) mean? "

Your logic fails because there are two ways to get each outcome. Say you have AcAs, then board could come AhAdx or AdAhx. So you get 288/117600=3/1225=48/19600 as given earlier.

Craig
#10
11-14-2002, 11:40 PM
 Guest Posts: n/a

Yes, that is precisely correct.

(48 choose 47) = (48 choose 1) = 48

This is a combinatorial identity, that is, (N choose K) = (N choose (N-K)).

Do you see why this must be true? Say you've got 48 balls, numbered from 1 to 48. If you choose 47 of them to take away, you can see what you did from a different perspective... that you chose 1 from 48 to leave. It follows then that if you have N differentiable objects, and you choose K of them, it's the same as if you "chose" (N-K) of them to not be chosen.

If you still don't see why this is true, please ask again, and I will try to provide a different example.

RMJ

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