Problem :
There are three traffic lights between your house and a friend's house. As you arrive at each light, it may be red (R), yellow (Y), or green (G).
a. List the sample space showing all possible sequences of red and green lights that could occur on a trip from your house to your friend's. (Example: RGG, which represents red at the first light and green at the other two) Assume that each element of the sample space is equally likely to occur.
b. What is the probability that on your next trip to your friend's house, you will have to stop for exactly one red light?
c. What is the probability that you will have to stop for at least one red light?