8. A random sample of 100 teenagers was surveyed, and the mean number of songs that they had downloaded from the iTunes store in the past month was 9.4 with the results considered accurate is within 1.4 (18 times out of 20).

a. What percent of confidence level is the result?

b. What is the margin of error?

c. What is the confidence interval? Explain.

9.

. The director of human resources for a large bank has compiled data on about 70 former employees at one of the banks call centers (see the Excel file Call Center Data). For each of the following, assume equal variances of the two populations.

a. Test the null hypothesis that the average length of service for males is the same as for females.

b. Test the null hypothesis that the average length of service for individuals without prior call center experience is the same as those with experience.

c. Test the null hypothesis that the average length of service for individuals with a college degree is the same as for individuals without a college degree.

d. Now conduct tests of hypotheses for equality of variances. Were your assumptions of equal variances valid? If not, repeat the test(s) for means using the unequal variance test.