Chapter 12: Problem 4
Explain the difference between \(\mu\) and \(\mu_{\bar{x}}\)
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Chapter 12: Problem 4
Explain the difference between \(\mu\) and \(\mu_{\bar{x}}\)
These are the key concepts you need to understand to accurately answer the question.
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A credit bureau analysis of undergraduate students credit records found that the average number of credit cards in an undergraduate's wallet was 4.09 ("Undergraduate Students and Credit Cards in 2004," Nellie Mae, May 2005 ). It was also reported that in a random sample of 132 undergraduates, the sample mean number of credit cards that the students said they carried was 2.6 . The sample standard deviation was not reported, but for purposes of this exercise, suppose that it was 1.2 . Is there convincing evidence that the mean number of credit cards that undergraduates report carrying is less than the credit bureau's figure of \(4.09 ?\)
What percentage of the time will a variable that has a \(t\) distribution with the specified degrees of freedom fall in the indicated region? (Hint: See discussion on page 496 ) a. 10 df, between -1.81 and 1.81 b. 24 df, between -2.06 and 2.06 c. 24 df, outside the interval from -2.80 to 2.80 d. 10 df, to the left of -1.81
In a study of computer use, 1,000 randomly selected Canadian Internet users were asked how much time they spend online in a typical week (Ipsos Reid, August 9,2005 ). The sample mean was 12.7 hours. a. The sample standard deviation was not reported, but suppose that it was 5 hours. Carry out a hypothesis test with a significance level of 0.05 to decide if there is convincing evidence that the mean time spent online by Canadians in a typical week is greater than 12.5 hours. b. Now suppose that the sample standard deviation was 2 hours. Carry out a hypothesis test with a significance level of 0.05 to decide if there is convincing evidence that the mean time spent online by Canadians in a typical week is greater than 12.5 hours. c. Explain why the null hypothesis was rejected in the test of Part (b) but not in the test of Part (a).
How much money do people spend on graduation gifts? In \(2007,\) the National Retail Federation (www.nrf.com) surveyed 2,815 consumers who reported that they bought one or more graduation gifts that year. The sample was selected to be representative of adult Americans who purchased graduation gifts in 2007 . For this sample, the mean amount spent per gift was \(\$ 55.05\). Suppose that the sample standard deviation was \$20. Construct and interpret a \(98 \%\) confidence interval for the mean amount of money spent per graduation gift in 2007 .
12.56 Speed, size, and strength are thought to be important factors in football performance. The article "Physical and Performance Characteristics of NCAA Division I Football Players" (Research Quarterly for Exercise and Sport [1990]: \(395-401\) ) reported on physical characteristics of Division I starting football players in the 1988 football season. The mean weight of starters on top-20 teams was reported to be \(105 \mathrm{~kg} .\) A random sample of 33 starting players (various positions were represented) from Division I teams that were not ranked in the top 20 resulted in a sample mean weight of \(103.3 \mathrm{~kg}\) and a sample standard deviation of \(16.3 \mathrm{~kg} .\) Is there sufficient evidence to conclude that the mean weight for non-top-20 team starters is less than \(105,\) the known value for top-20 teams?
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