We have a system consisting of four components. Each component functions or fails, each independently of the others. The entire system functions if A and B function, along with at least one of C or D. That is, if A or B fail, the entire system fails... but C can fail as long as A, B and D function. Now, suppose A functions with probability 0.8, B functions with probability 0.9, C functions with probability 0.7 and D functions with probability 0.75.
a.) What is the probability that the entire system functions?
b.) If the entire system functions, what is the probability that component C functioned?