178 CHAPTER 4 Probability c. The probability that all three children are girls. d. The probability that at least one of the children is a girl. 8. Births in Vietnam In Vietnam, the probability of a baby being a boy is 0.526 (based on the data available at this writing). For a family having four children, find the following. a. The probability that the first child is a girl. b. The probability that all four children are girls. c. The probability that all four children are boys. d. The probability that at least one of the children is a girl. 9. California Lottery In the California Daily 4 lottery, the probability of winning with one ticket is 0.0001. Someone buys one ticket on each of 10 different days. a. What is the probability that all ten tickets are losing tickets? b. What is the probability that at least one of the tickets is a winner? 10. At Least One Correct Answer If you make random guesses for 10 multiple choice SAT test questions (each with five possible answers), what is the probability of getting at least 1 correct? If these questions are part of a practice test and an instructor says that you must get at least one correct answer before continuing, is there a good chance you will continue? 11. At Least One Defective iPhone It has been reported that 20% of iPhones manufactured by Foxconn for a product launch did not meet Apple’s quality standards. An engineer needs at least one defective iPhone so she can try to identify the problem(s). If she randomly selects 15 iPhones from a very large batch, what is the probability that she will get at least 1 that is defective? Is that probability high enough so that she can be reasonably sure of getting a defect for her work? 12. Drunk Driving In the United States, 31% of road crash deaths involve alcohol (based on data from the Global Status Report on Road Safety). What is the probability that among five randomly selected road crash deaths, at least one involved alcohol? If a researcher plans to conduct an in-depth study of road crash deaths that involve alcohol, can she be reasonably confident that the five road crash deaths will include at least one that involved alcohol? Denomination Effect. In Exercises 13–16, use the data in the following table. In an experiment to study the effects of using four quarters versus a $1 bill, some college students were given four quarters and others were given a $1 bill, and they could either keep the money or spend it on gum. The results are summarized in the table (based on data from “The Denomination Effect,” by Priya Raghubir and Joydeep Srivastava, Journal of Consumer Research, Vol. 36). Purchased Gum Kept the Money Students Given Four Quarters 27 16 Students Given a $1 bill 12 34 13. Denomination Effect a. Find the probability of randomly selecting a student who spent the money, given that the student was given four quarters. b. Find the probability of randomly selecting a student who kept the money, given that the student was given four quarters. c. What do the preceding results suggest? 14. Denomination Effect a. Find the probability of randomly selecting a student who spent the money, given that the student was given a $1 bill.
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