Chapter 8.2, Problem 9E

For Exercises 1 through 25, perform each of the following steps.

a. State the hypotheses and identify the claim.

b. Find the critical value(s).

c. Compute the test value.

d. Make the decision.

e. Summarize the results.

Use diagrams to show the critical region (or regions), and use the traditional method of hypothesis testing unless otherwise specified.

9. Telephone Calls A researcher knew that before cell phones, a person made on average 2.8 calls per day. He believes that the number of calls made per day today is higher. He selects a random sample of 30 individuals who use a cell phone and asks them to keep track of the number of calls that they made on a certain day. The mean was 3.1. At α = 0.01 is there enough evidence to support the researcher's claim? The standard deviation for the population found by a previous study is 0.8. Would the null hypothesis be rejected at α = 0.05?