I don't have the time right now to go through the calculations myself, but the technique you'd use here is counting. Figure out how many flops satisfy your conditions then divide by the total number of flops (50 * 49 * 48, if you know only 2 cards) and you've got your chance.

Give it a crack on #1 and I'll come back and see how you fare. Or don't and maybe some day I'll come back and do it for you.