Wing cracks, in the inspection of commercial aircraft, are reported as nonexistent, detectable, or critical. The history of a certain fleet shows that 70% of the planes inspected have no wing cracks, 25% have detectable wing cracks, and 5% have critical wing cracks. For the next five planes inspected, find the probability that
a One has a critical crack, two have detectable cracks, and two have no cracks.
b At least one critical crack is observed.