You are working at a firm that conducts independent testing for heavy industry. Recently, an automobile manufacturer has been in the news for complaints about the highway gas mileage of their latest model minivan. You receive a contract from a consumer action group to test and write a report on the company's claim that its minivans get 28 miles per gallon on the highway. The car company agrees to allow you to randomly select 35 low-mileage fleet minivans to test their highway mileage. Your test results gave you the following data:

29.7 24.5 27.1 29.8 29.2 27.0 27.8 24.1 29.3

25.9 26.2 24.5 32.8 26.8 27.8 24.0 23.6 29.2

26.5 27.7 27.1 23.7 24.1 27.2 25.9 26.7 27.8

27.3 27.6 22.8 25.3 26.6 26.4 27.1 26.1

Calculate a 95% confidence interval around your sample mean. Include your calculations.

Interpreting the Confidence Interval

Is the company's claimed mean inside your confidence interval?

What does that result indicate about the company's claim?

Hypothesis Testing: Two-Tail Test and One-Tail Test

Calculating a Two-Tail Test

List the null and alternative hypotheses for the two-tail test for the mean. Calculate the observed value of the test statistic and the associated p-value. Include your calculations.

Interpreting the Two-Tail Test

Is the observed test statistic in the critical region?Is the p-value higher or lower than your alpha?

Calculating a One-Tail Test

List the null and alternative hypotheses for the one-tail test of the mean. Calculate the observed value of the test statistic and the associated p-value. Include your calculations.

Interpreting the One-Tail Test

Is the observed test statistic in the critical region?Will the p-value be higher or lower than your alpha?