Suppose 1000 iPhones are produced at a factory today. Management would like to ensure that the phones’ display screens meet their quality standards before shipping them to retail stores. Because it takes about 10 minutes to inspect an individual phone’s display screen, managers decide to inspect a sample of 20 phones from the day’s production.

a. Explain why it would be difficult for managers to inspect an SRS of 20 iPhones that are produced today.

b. An eager employee suggests that it would be easy to inspect the last 20 iPhones that were produced today. Why isn’t this a good idea?

c. Another employee recommends a different sampling method: Randomly choose one of the first 50 iPhones produced. Inspect that phone and every fiftieth iPhone produced afterward. (This method is known as systematic random sampling.) Explain carefully why this sampling method is not an SRS.