The outcome of chance events in a fantasy role playing game is determined by rolling a dice with anywhere from 4 to 20 sides. Suppose you roll a 16 sided die 5 times and observe the number on top of the die.

a. How many possible outcomes are there for these 5 rolls?

b. In how many of the outcomes in part a do the 5 rolls produce 5 different numbers?

c. What is the probability that at least 2 of the rolls are the same?