4.4. Consider two machines, operating simultaneously and independently, where both machines have an exponentially distributed time to failure with mean 1/μ (p. is the failure rate). There is a single repair facility, and the repair times are exponentially distributed with rate A.

(a) In the long run, what is the probability that no machines are operating?

(b) How does your answer in

(a) change if at most one machine can operate, and thus be subject to failure, at any time?