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 Originally Posted by sed
I figured there was at least a 30% chance that he was full of crap. On the chance he actually hit something I have about 9 outs to catch either a higher pair or runner runner a flush. Add those up and thats better than a coinflip to win the hand.
First, the runner runner chance is not nearly equal to 3 outs -- 10/47 * 9/46 = 0.0416281221. This is closer to 1 additional out than 3. Therefore -- you probably have 7 clean outs to improve if he has a pair, or around a 28% chance. So, let's examine the possibilities. First, assign X as the probability of him having nothing (less than a pair), making (1-x) the chance of him having at least a pair.
If he has at least a pair, p(1-x):
He has 5 outs to improve to 2 pair or better, or about a 20% chance. However, there are rare instances where he will improve and you will still win (you improve with runner runner flush, 2 pair or trips). We already figured out the chance of runner runner flush, and runner runner 2 pair or better is about another 1% added on -- so about 5% of the time he improves, you will still win. This means his chance of improving to the winning hand, given that he has at least a pair on the flop, is about 19%.
If he doesn't improve -- 80% of the time -- you will win if you you hit your 7 outs. This will happen about 28% of the time. This means, if he has at least a pair on the flop and it doesn't improve by the river, he will still win about 58% of the time.
So, the total percentage of hands he will win, given that he has a pair on the flop, is about 77%.
If he doesn't have a hand after the flop, P(x):
He will improve 24% of the time to at least 1 pair by the river. Of those times he bluffs the flop, and still improves, you will also improve 28% of the time -- so he will only improve to win about 17% of the time given that he was bluffing on the flop. Obviously, if he was bluffing, and doesn't improve, you win, as you have the nuts high card.
So, the percentage of your losing here is approximately equal to (1-x)(.77) + (x)(.17), or the probability of him winning if he wasn't bluffing the flop and the probability of him sucking out even if he was bluffing the flop. (Conversely, P(you call and win) = 1 - ((1-x)(.77) + (x)(.17)). If you want to win more than 50% of the time, faced with this situation, you should have a read suggesting that he is bluffing more than 45% of the time, because if he bluffs less than 45% of the time here, he's the favorite.
Please correct any of my assumptions, math or reasoning if you see errors. I'm interested in this sort of question, and new to this sort of analysis. Thanks.
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