Monitoring quality. A cell phone manufacturer samples cell phones from the assembly to test. She noticed that the number of faulty cell phones in a production run of cell phones is usually small and that the quality of one day’s run seems to have no bearing on the next day.

a) What model might you use to model the number of faulty cell phones produced in one day?

She wants to model the time between the events of producing a faulty phone. The mean number of defective cell phones is 2 per day.

b) What model would you use to model the time between events?

c) What would the probability be that the time to the next failure is 1 day or less?

d) What is the mean time between failures?