A system has four computers. Computer 1 works with a probability of 0.88; computer 2 works with a probability of 0.78; computer 3 works with a probability of 0.92; computer 4 works with a probability of 0.85. Suppose that the operations of the computers are independent of each other.
(a) Suppose that the system works only when all four computers are working. What is the probability that the system works?
(b) Suppose that the system works only if at least one computer is working. What is the probability that the system works?
(c) Suppose that the system works only if at least three computers are working. What is the probability that the system works?