Plot the reading time using a normal probability plot or boxplot. Do the data appear

a. Place a 99 confidence interval on the average number of miles driven, m, prior to

the tires wearing out. b. Is there significant evidence a ⫽ .01 that the manufacturer’s claim is false? What is the level of significance of your test? Interpret your findings. 5.42 Refer to Exercise 5.41. Using the Minitab output given, compare your results to the results given by the computer program. a. Does the normality assumption appear to be valid? b. How close to the true value were your bounds on the p-value?

c. Is there a contradiction between the interval estimate of m and the conclusion

reached by your test of the hypotheses? Env. 5.43 The amount of sewage and industrial pollutants dumped into a body of water affects the health of the water by reducing the amount of dissolved oxygen available for aquatic life. Over a 2-month period, 8 samples were taken from a river at a location 1 mile downstream from a sewage treatment plant. The amount of dissolved oxygen in the samples was determined and is reported in the following table. The current research asserts that the mean dissolved oxygen level must be at least 5.0 parts per million ppm for fish to survive. Sample 1 2 3 4 5 6 7 8 n s Oxygen ppm 5.1 4.9 5.6 4.2 4.8 4.5 5.3 5.2 8 4.95 .45 a. Place a 95 confidence on the mean dissolved oxygen level during the 2-month period. b. Using the confidence interval from a, does the mean oxygen level appear to be less than 5 ppm?

c. Test the research hypothesis that the mean oxygen level is less than 5 ppm. What is

the level of significance of your test? Interpret your findings. Env. 5.44 A dealer in recycled paper places empty trailers at various sites. The trailers are gradually filled by individuals who bring in old newspapers and magazines, and are picked up on several schedules. One such schedule involves pickup every second week. This schedule is desirable if the average amount of recycled paper is more than 1,600 cubic feet per 2-week period. The dealer’s records for eighteen 2-week periods show the following volumes in cubic feet at a particular site: 1,660 1,820 1,590 1,440 1,730 1,680 1,750 1,720 1,900 1,570 1,700 1,900 1,800 1,770 2,010 1,580 1,620 1,690 ⫽ 1,718.3 and s ⫽ 137.8

a. Assuming the eighteen 2-week periods are fairly typical of the volumes throughout

the year, is there significant evidence that the average volume m is greater than 1,600 cubic feet? y y 40 35 30 25 Mil e s Boxplot of tire data Test of normality for tire data .999 .99 .95 .80 .50 .20 .05 .01 .001 Probability

25 30

35 40 Miles Test of mu ⫽ 35.00 vs mu ⬍ 35.00 Var iable N Mean StDev SE Mean T P 99.0 CI Miles 15 31.47 5.04 1.30 ⫺2.71 0.0084 27.59, 35.3