You have a bag of chips and they come in the below hues: 

 red, blue, green, purple, and yellow.

a. If the bottom chip in a stack must be either red or blue, how many possible combinations of two chips are there?
b. How many distinct stacks of three chips can be created if the bottom chip must be either red or blue and the top chip must be either green, purple or yellow? What is the connection between this issue and the one before it?
c. In how many distinct three-chip stacks is it possible to find a repetition of colour? What about a stack of four chips?
d. Let's say you intended to stuff your pocket with three chips of varying hues. How many options are available to you? Is there any way to have four distinct hues of chips? What connections can you make between these issues?