An archer hits a bull's-eye with a probability of 0.09. and the results of different attempts can be taken to be independent of each other, [f the archer shoots nine arrows, calculate the probability that:
(a) Exactly two arrows score bull's-eyes.
(b) At least two arrows score bull's-eyes.
What is the expected number of bull's-eyes scored? (This problem is continued in Problems 3.2.5 and 3.5.3.)