720 CHAPTER 14 Statistical Process Control 5. Service Times A manager of a McDonald’s franchise has developed a service criterion whereby a dinner order is considered to be defective if it takes longer than 180 seconds. Listed below are numbers of such defects among groups of 50 different customers on each of several consecutive days (based on Data Set 36 “Fast Food” in Appendix B). Construct an appropriate control chart and determine whether the process is within statistical control. What should the manager conclude from the result? 19 21 21 17 15 12 24 26 28 21 22 23 21 20 25 Cumulative Review Exercises 1. Federal Criminal Defendants The following graph depicts results from a study of defendants in federal crime cases (based on data from the Administrative Office of the U.S. Courts). a. If a defendant is randomly selected what is the probability that this person had their case dismissed before going to trial? b. If a defendant goes to trial, what is the probability of an acquittal from the trial? c. If a defendant is randomly selected, what is the probability of getting someone who went to trial and was subsequently convicted? d. If three defendants are randomly selected, what is the probability that they all pleaded guilty? e. If a defense attorney is assigned a random defendant, what seems like a reasonable strategy for the client? 2. Are Nuclear Plants Safe? In a Gallup poll of 1038 adults, 47% said that nuclear plants are safe, 49% said that they are not safe, and 4% had no opinion. Construct a 95% confidence interval estimate of the proportion of all adults who say that nuclear plants are safe. Based on the result, can we conclude that fewer than half of all adults say that nuclear plants are safe? 3. Are Nuclear Plants Safe? Use the data from the preceding exercise to test the claim that fewer than half of all adults say that nuclear plants are safe. Use a 0.05 significance level. Does the conclusion contradict the conclusion from the preceding exercise? 4. Are Nuclear Plants Safe? Using the survey results from Exercise 2 and ignoring those respondents with no opinion, is the following graph somehow misleading? If so, how?
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