Chapter 9.3, Problem 9.58E

a)

To determine

To explain which one should recommend from significance test or confidence interval.

Answer to Problem 9.58E

It is best to perform significance test.

Explanation of Solution

Given:

The population proportion is 85%.

We have to check whether proportion of 85% is actually correct. This can be done by testing a claim and a confidence interval. As estimate of 85% is already given, it is better to go for significance test.

b)

To determine

To explain whether to generalize results to population of all cars on the road.

Answer to Problem 9.58E

No.

Explanation of Solution

Given:

The population proportion is 85%.

No, their results cannot be generalized, because the data only consists of cars that were brought in for oil changes. However not all cars will be brought in for oil changes and therefore not all cars have a chance of being in the sample, which means that the sample is not a random sample of the population.