Answer
See below.
Work Step by Step
a) In this case the events are independent: $\frac{4}{52}\frac{4}{52}\frac{4}{52}=\frac{1}{2197}$
b) In this case the events are not independent: the first one has probability $\frac{4}{52}$; the second one has probability $\frac{4}{51}$; and the third one has probability $\frac{4}{50}$. Thus the probability is: $\frac{4}{52}\frac{4}{51}\frac{4}{50}=\frac{8}{16575}$
