An electronics company advertises that the battery life of its new smart phone with normal usage averages 72 hours. The company says this is one of the desirable characteristics of the phone which makes the phone a better choice compared to competitor phones. Recently, the company has received an unusually large number of complaints regarding the battery life. Many customers indicated the battery needed to be recharged long before the advertised average life. To check if the average battery life equals 72 hours, the company randomly selected 36 phones and tested the battery life. The sample produced a mean battery life of 69.5 hours with a standard deviation of 5 hours. Answer the following questions:
a. Perform the appropriate test to determine if the average battery life differs from the advertised life of 72 hours. Use the test statistic method to perform the test. Alpha for the test is .05. Be sure to include all required steps of the hypothesis test procedure as outlined and performed in class.
b. Compute a 95% confidence interval estimate for the mean battery life. How does your confidence interval support the conclusion of your hypothesis test?