A+ Answers

10.9 A problem with a telephone line that prevents a customer from receiving or making calls is upsetting to both the customer and the telephone company. The file Phone contains samples of 20 problems reported to two different offices of a telephone company and the time to
clear these problems (in minutes) from the customers’ lines:
Central Office I Time to Clear Problems (minutes)
1.48 1.75 0.78 22.85 0.52 1.60 4.15 3.97 1.48 3.10
1.02 0.53 0.93 1.60 0.80 1.05 6.32 3.93 5.45 0.97
Central Office II Time to Clear Problems (minutes)
7.55 3.75 0.10 1.10 0.60 0.52 3.30 2.10 0.58 4.02
3.75 0.65 1 92 0.60 1.53 4.23 0.08 1.48 1.65 0.72
a. Assuming that the population variances from both offices are equal, is there evidence of a difference in the mean waiting time between the two offices? (Use a=0.05)
b. Find the p-value in (a) and interpret its meaning.
c. What other assumption is necessary in (a)?
d. Assuming that the population variances from both offices are equal, construct and interpret a 95% confidence interval estimate of the difference between the population means in the two offices.
10.11 An important feature of digital cameras is battery life, the number of shots that can be taken before the battery needs to be recharged. The file Digital cameras contains the battery
life of 29 subcompact cameras and 16 compact cameras. (Data extracted from “Digital Cameras,” Consumer Reports, July 2009, pp. 28–29.)
a. Assuming that the population variances from both types of digital cameras are equal, is there evidence of a difference in the mean battery life between the two types of digital cameras (a =0.05)
b. Determine the p-value in (a) and interpret its meaning.
c. Assuming that the population variances from both types of digital cameras are equal, construct and interpret a 95% confidence interval estimate of the difference between the population mean battery life of the two types of digital cameras.
10.21 In industrial settings, alternative methods often exist for measuring variables of interest. The data in measurements (coded to maintain confidentiality) represent measurements in-line that were collected from an analyzer during the production process and from an analytical lab.
a. At the 0.05 level of significance, is there evidence of a difference in the mean measurements in-line and from an analytical lab?
b. What assumption is necessary about the population distribution in order to perform this test?
c. Use a graphical method to evaluate the validity of the assumption in (a).
d. Construct and interpret a 95% confidence interval estimate of the difference in the mean measurements in-line and from an analytical lab.
10.23 In tough economic times, the business staff at magazines are challenged to sell advertising space in their publications. Thus, one indicator of a weak economy is the decline in the number of “ad pages” that magazines have sold. The file add pages contains the number of ad pages
found in the May 2008 and May 2009 issues of 12 men’s magazines. (Data extracted from W. Levith, “Magazine Monitor,” Mediaweek, April 20, 2009, p. 53.)
a. At the 0.05 level of significance, is there evidence that the mean number of ad pages was higher in May 2008 than in May 2009?
b. What assumption is necessary about the population distribution in order to perform this test?
c. Use a graphical method to evaluate the validity of the assumption in (b).
d. Construct and interpret a 95% confidence interval estimate of the difference in the mean number of ad pages in men’s magazines between May 2008 and May 2009.
10.48 An important feature of digital cameras is battery life, the number of shots that can be taken before the battery needs to be recharged. The file Digital cameras contains battery
life information for 29 subcompact cameras and 16 compact cameras. a. Is there evidence of a difference in the variability of the battery life between the two types of digital cameras?
(Use a = 0.05 )
b. Determine the p-value in (a) and interpret its meaning.
c. What assumption about the population distribution of the two types of cameras is necessary in (a)? Is the assumption valid for these data?
d. Based on the results of (a), which t test defined in Section
10.1 should you use to compare the mean battery life of the two types of cameras?