Consider the system of components connected as in the accompanying picture. Components 1 and 2 are connected in parallel, so that the subsystem works if and only if either 1 or 2 works; since 3 and 4 are connected in series, that subsystem works if and only if both 3 and 4 work. If components work independently of one another and P (components works) = 0.9 and the whole system works if and only if both subsystems work, calculate P(system works)