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Chapter 8: Q 30. (page 522)
High tuition costs Glenn wonders what proportion of the students at his college believe that tuition is too high. He interviews an SRS of of the students and finds of those interviewed think tuition is too high.
All the conditions are met in given case.
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Reporting cheating What proportion of students are willing to report cheating by other students? A student project put this question to an SRS of undergraduates at a large university: 鈥淵ou witness two students cheating on a quiz. Do you go to the professor?鈥� Only answered 鈥淵es.鈥� Assume the conditions for inference are met.
a. Determine the critical valuefor a confidence interval for a proportion.
b. Construct a confidence interval for the proportion of all undergraduates at this university who would go to the professor.
c. Interpret the interval from part (b).
A Gallup poll found that only of American adults expect to inherit money or valuable possessions from a relative. The poll鈥檚 margin of error was 卤3 percentage points at a confidence level. This means that
a. the poll used a method that gets an answer within 3% of the truth about the population of the time.
b. the percent of all adults who expect an inheritance must be between and .
c. if Gallup takes another poll on this issue, the results of the second poll will lie between and .
d. there鈥檚 a 95% chance that the percent of all adults who expect an inheritance is between
25% and 31%.
e. Gallup can be 95% confident that between 25% and 31% of the sample expect an inheritance.
Estimating BMI The body mass index (BMI) of all American young
women is believed to follow a Normal distribution with a standard deviation of about . How large a sample would be needed to estimate the mean BMI 渭 in this population to within with confidence?
One reason for using a t distribution instead of the standard Normal distribution to find critical values when calculating a level C confidence interval for a population mean is that
a. can be used only for large samples.
b. requires that you know the population standard deviation .
c. requires that you can regard your data as an SRS from the population.
d. requires that the sample size is less than of the population size.
e. a critical value will lead to a wider interval than a critical value.
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 true proportion p of all 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.
e.
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