Probability of flopping 1 card flush draw?

[Mark1808]

I come up with a number I think is too high and I think it has to do with inclusion - exclusion.

Probability you hold two diamonds, that you will flop 2 diamonds =

P(1st and 2nd cards are diamonds)= 11/50 * 10/49 = 4.49% or
P (2nd & 3rd cards are diamonds) = 11/49 * 10/48 = 4.68% or
P (1st & 3rd card are diamonds) = 11/50 * 10/48 = 4.58%

P(of floppin 1 card draw) = 4.49 + 4.68 + 4.58 = 13.75%

Then probaility of flopping flush = 11/50 * 10/49 * 9 /48 = .84%

I'm wondering if I should be using the choose function to calculate these?