How to Solve Flop to River with Differing Outs?

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What is the general proceedure for using the combinations method to determine the probability of hitting either one or two of your outs when the number of outs is different on the flop and turn? For example, a set, which has 7 outs on the flop and 10 outs on the turn.

In "Hold'em's Odd(s) Book", Petriv solves this problem by adding the probability of making quads or a full house with the 7 flop outs to the probability of making a running pair.

Is there a more general way to determine the flop to river probabilities (hitting 1 out, hitting 2 outs, hitting 1 or 2 outs) if the flop outs are X and the turn outs are Y ?

Please show your work [img]/images/graemlins/smile.gif[/img],
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