Do young children use cell phones? Apparently so, according to a recent study (A. Ross, "Message to Santa; Kids Want a Phone," Palm Beach Post, December 16, 2008,pp. 1A, 4A), which stated that cell phone users under 12 years of age averaged 137 calls per month as compared to 231 calls per month for cell phone users 13 to 17 years of age. No sample sizes were reported. Suppose that the results were based on samples of 50 cell phone users in each group and that the sample standard deviation for cell phone users under 12 years of age was 51.7 calls per month and the sample standard deviation for cell phone users 13 to 17 years of age was 67.6 calls per month.
a. Using a 0.05 level of significance, is there evidence of a difference in the variances of cell phone usage between cell phone users under 12 years of age and cell phone users 13 to 17 years of age?
b. On the basis of the results in (a), which t test defined in Section 10.1 should you use to compare the means of the two groups of cell phone users? Discuss.