[LetYouDown]

I believe you're double counting:

[C(4,1) * C(4,1) * C(4,1) * C(47,2)]/C(50,5) = 3.265%

If your opponent held A-K, I think it should be:

[C(4,1) * C(3,1) * C(3,1) * C(45,2)]/C(48,5) = 2.08%

Although that would include the times you lose to a boat/quads.