Suppose we have a bag with $10$ slips of paper in it. Eight slips have a $3$ on them and the other two have a $9$ on them.
a) What is the expected value of the number shown when we draw a single slip of paper?
b) What is the expected value of the number shown if we add one additional $9$ to the bag?
c) What is the expected value of the number shown if we add two additional $9$'s (instead of just one) to the bag?
