2) A high-performance airplane contains three identical computers. Only one is used to operate the aircraft; the remaining two are spares that can be activated in case the primary system fails. During one hour of operation the probability of a failure of the primary computer (or any of the activated spare systems) is 0.0005. Assuming that each hour represents an independent trial:

a) What is the average time for all three computers to fail?

b) What is the probability that all three computers will fail in a 5-hour flight?