Correction
I avoided double counting cases like 458 and 584, but I am still double counting cases like 454. This is because when we say there are 4*4*48 ways to get 45x, some of those 48 cards will be a 4 or a 5, and those cards were already counted in the 4*4. So we have to go a step further and separate out the cases where there is a pair on the flop. Sooooo...proceding as before:
45x where x is anything:
4*4*42 + 6*4 + 6*4 = 720.
The 6*4 correspond to a pair of 4s or a pair of 5s.
58x where x is anything but 4:
4*4*38 + 6*4 + 6*4 = 656
89x where x is anything but 5:
4*4*38 + 6*4 + 6*4 = 656
(720+656+656)/C(50,3) = 10.4%.
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