Chapter 4.1, Problem 17E

To determine

To explain why would it be difficult for mangoes to inspect an SRS of 20 iPhones.

Explanation of Solution

Given Information:

Thousand iPhones are produced at factory today.

Assuming none of the phones can be shipped until after the inspection, inspecting a random sample of 20 phones could hold up the shipping process. Additionally, in order to obtain a random sample, the phones must be numbered in some way. Keeping track of the ordering of 1000 phones may be difficult.

b.

To determine

To explain why the given idea is not good.

Explanation of Solution

Given Information:

The idea is to inspect the last 20 iPhones that were produced that day.

Convenience samples are almost guaranteed to show bias. It is unlikely that last 20 iPhones produced are representative of all the iPhones produced during the day. It is possible that the quality of the iPhones produced might change in between the production of 1000 iPhones during the day. Hence the last 20 iPhones manufactured is not a good sampling for the quality check of the day’s production and it would not be a good idea to inspect last 20 iPhones.

c.

To determine

To explain why the given method is not an SRS.

Explanation of Solution

Given Information:

Another employee recommends inspecting every fifteenth iPhone that is being produced.

A simple random sample (SRS) of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected. Inspecting every 49th iPhone does not form an SRS because each sample of 20 iPhones does not have the same probability of being selected. The 20 iPhones that are sampled will be the 49th, 99th,..., 999th and others have no chance of being sampled..