Calculate odds

Suppose we are dealing 3 cards out (which is know as a flop) from a 52 cards deck:

1.Calculate the odds of having 3 different cards on the flop
2. Calculate the odds of having 3 different cards on the flop if I hold 2 cards that are different from the cards on the flop
2. Calculate the odds of having 3 different cards on the flop if I hold 4 cards that are different from the cards on the flop