Simple way to find combinations of hands?

[Popinjay]

This is how I was I was calc-ing combinations. Preflop how may combos of AA are out there? I did (4 aces * 3 aces)/2 = 6. Then for AK I did (8 aces or kings * 4 ace/king)/2 = 16. That works right? but then say on the flop there is a King on the board and you have AA. How many AK are out there? (5 aces/kings * what?)/2

I don't think my method works for that on the flop. Can someone show me the easiest while still accurate method for figuring out hand combinations?