The probability of flopping a set in holdem

Hi

I was just trying to work out the probability of flopping a set on the flop in texas holdem but don't know if its exactly. I'm assuming only a set and not four of a kind.

My workings:

P(Flopping a Set)=[(2/50)*(48/49)*(47/48)]+[(48/50)*(2/49)*(47/48)]+[(48/50)*(47/49)*(2/48)]

= 0.11510204 or about odds of 8.688:1

Does that seem correct?

what about after the river?

What about hiting a set after the final fifth card?

In other words if I go all in preflop with a pocket pair . . . what are my chances of hitting my set after all cards are on the table?