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Chapter 8: Q.3.1 (page 494)
The company’s customer satisfaction survey.
In the company’s prior-year survey, 80% of customers surveyed said they were “satisfied” or “very satisfied.” Using this value as a guess for pˆ, find the sample size needed for a margin of error of 3% at a 95% confidence level.
The sample size is 683
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Many television viewers express doubts about the validity of certain commercials. In an attempt to answer their critics, Timex Group USA wishes to estimate the proportion of consumers who believe what is shown in Timex television commercials. Let represent the true proportion of consumers who believe what is shown in Timex television commercials. What is the smallest number of consumers that Timex can survey to guarantee a margin of error of or less at a confidence level?
(a)
(b)
(c)
(d)
(c)
In each of the following situations, discuss whether it would be appropriate to construct a one-sample interval to estimate the population mean.
(a) We want to estimate the average age at which U.S. presidents have died. So we obtain a list of all U.S. presidents who have died and their ages at death.
(b) How much time do students spend on the Internet? We collect data from the members of our AP Statistics class and calculate the mean amount of time that each student spent on the Internet yesterday.
(c) Judy is interested in the reading level of a medical journal. She records the length of a random sample of words from a multipage article. The Minitab histogram below displays the data.
Got shoes? The class in Exercise 1 wants to estimate the variability in the number of pairs of shoes that female students have by estimating the population variance .
57. Critical values What critical value t* from Table B would you use for a confidence interval for the population mean in each of the following situations?
(a) A confidence interval based on observations.
(b) A confidence interval from an SRS of observations.
58. Critical values What critical value t* from Table should be used for a confidence interval for the population mean in each of the following situations?
(a) A confidence interval based on n observations.
(b) A confidence interval from an SRS ofobservations.
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