For Exercise 21.1, see page 499; for Exercise 21.2, see page 505; and for Exercise 21.3, see page 509.
21.4 Bike riding. In 2012, the National Highway Traffic Safety Administration (NHTSA) of the U.S. Department of Transportation conducted the National Survey of Bicyclist and Pedestrian Attitudes and Behaviors. A total of 7509 individuals aged 16 years and older participated in this survey. Of these 7509 individuals, 2580 individuals reported that they rode a bicycle within the past year. Of these self-reported bicycle riders, 1187 said they had never worn a helmet when riding a bicycle. Based on this information, we know the sample proportion, , of bicycle riders from this survey who have never worn a helmet is
(a) 0.460.
(b) 0.344.
(c) 0.158.
(d) 0.013.
21.5 Saving for retirement. In 2014, a leading financial services provider conducted a survey in order to determine how Americans are planning for retirement. Of the 1017 adults aged 18 years and older who were included in the survey, 214 said they were currently not saving anything for retirement. Based on this information, the 95% confidence interval for the proportion of all adults who are currently not saving for retirement would be
(a) 0.155 to 0.265.
(b) 0.185 to 0.235.
(c) 0.197 to 0.223.
(d) 0.200 to 0.220.
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21.6 Computer use. A random sample of 197 12th-grade students from across the United States was surveyed, and it was observed that these students spent an average of 23.5 hours on the computer per week, with a standard deviation of 8.7 hours. If we plan to use these data to construct a 99% confident interval, the margin of error will be approximately
(a) 0.07.
(b) 0.62.
(c) 1.6.
(d) 8.7.
21.7 Anxiety. A particular psychological test is used to measure anxiety. The average test score for all university students nationwide is 85 points. Suppose a random sample of university students is selected and a confidence interval based on their mean anxiety score is constructed. Which of the following statements about the confidence interval is true?
(a) The resulting confidence interval will contain 85.
(b) The 95% confidence interval for a sample of size 100 will generally have a smaller margin of error than the 95% confidence interval for a sample of size 50.
(c) For a sample of size 100, the 95% confidence interval will have a smaller margin of error than the 90% confidence interval.
21.8 Pigs. A 90% confidence interval is calculated for a sample of weights of 135 randomly selected pigs, and the resulting confidence interval is from 75 to 90 pounds. Will the sample mean weight (from this particular sample of size 135) fall within the confidence interval?
(a) No.
(b) Yes.
(c) Maybe.