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If you are up against a donkey who will not lay down TPTK and he bets 10 into a 30 dollar pot on the flop and you both have 200 behind you call because you can bust him if you hit.


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Here's the math:
There is $40 in the pot now + $200 left in the bettor's stack. There is $240 for you to win, and hitting your set is 22:1 if you only factor in seeing the next card. Therefore you have 24:1 implied odds and you have a call here. Something else you may want to consider is whether or not you will see both cards. If you are on the flop and know you will see the river, the odds of you hitting your set are actually 10.88:1 meaning you have a huge call here.

I always keep a little cheat sheet with me that gives the odds against hitting any number of outs. PM me and I'll send it to you.