What is the probability that the next iphone 7 buyer

an AppleCare extended warranty. What is the probability that the next iPhone 7 buyer will
purchase an AppleCare extended warranty? (Hint: use the law of total probability.)
a. 0.45
b. 0.50
c. 0.55
d. 0.60
19. Continuing the last question, if the next buyer is known to have purchased an AppleCare
extended warranty, how likely is it that he or she has bought the 4.7-inch iPhone 7 model?
(Hint: use Bayes’ Theorem.)

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20. The above figure shows a system that consists of four components. Because components 1 and
2 are connected in parallel, the subsystem (1-2) works if at least one of the two components
works. Similarly, components 3 and 4 are connected in parallel in the subsystem (3-4), whose
functioning thus requires that one or both of components 3 and 4 work. The two subsystems,
(1-2) and (3-4), are connected in series; therefore, both subsystems must work for the whole
system to work. Suppose the components work independently of one another, and each
component works with probability 0.8. What is the probability that the whole system works?
a. 0.4096
b. 0.9216
c. 0.9600
d. 0.9984
b.
5