1. Defective computer disks are known to occur with a probability of 0.1. A ran dom sample of five disks is taken.
(a) Find the probability that at least one disk is defective.
(b) Find the probability that exactly two disks are defective.
2. The lifetime of a particular brand of computer is exponentially distributed with an average lifetime of 3.2 years.
(a) Find the probability that a randomly selected computer of this brand will have failed within 3 years.
(b) At what lifetime would 90% of all of this brand of computer have failed?