Holdem Math

[SteveS]

Is the expectation of catching an A or K on the flop in holdem if you have A/K:

6/50 + 6/49 + 6/48 = 18/147 = 12.25% ?

If not please help me understand the math.

Same question as it applies to Omaha if you hold A2XX, what is the chance you would be counterfeited on flop? ...on the next two cards?

Is it:

6/48 + 6/47 + 6/46 = 18/141 = 12.75% ?

And then to end: 30/230 = 13.0% ?

If not, please show me how to calculate this. I would really like to learn the math.