How To Calculate Odds of A, K, Q, or J Hitting

[bugeyebug]

I was told recently that the odds of an A, K, Q, and/or J hitting on the flop is 70% or so. This seems high to me, but another knowledgable person said it sounds right to them.

I'd like to learn how to make this calculation, but am getting lost in the math.

I know what two of the 52 cards (mine) are, and let's assume I don't have an A, K, Q, or J in my hand. This leaves 50 unaccounted for cards in the deck, of which there are 4 possible aces, 4 possible kings, 4 possible queens, and 4 possible jacks.

If I deal the first card of the flop, this means I have a (4+4+4+4)/50 chance of hitting an A, K, Q, or J, right? This is 32%.

Now, when I turn over the next card of the flop... here is where I get lost in the math. Is it 16/49? If so, then how do I combine it with the 32% number to get the "and/or" probability.

Then when I add the third card of the flop, is it 16/48?

Help! Can someone help me walk through this?
Cheers,
Bug