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Chapter 8: Q 38. (page 522)
More cheating Refer to Exercise 36. Calculate and interpret the standard error of for these data.
The value of standard error is.
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Suppose we want a 90% confidence interval for the average amount spent on books by freshmen in their first year at a major university. The interval is to have a margin of error of at most \(2. Based on last year鈥檚 book sales, we estimate that the standard deviation of the amount spent will be close to \)30. The number of observations required is closest to which of the following?
a.
b.
c.
d.
e.
t time When constructing confidence intervals for a population mean, we almost always use critical values from a t distribution rather than the standard Normal distribution.
a. When is it necessary to use a t critical value rather than a z critical value when constructing a confidence interval for a population means?
b. For a particular level of confidence, explain what happens to the t critical values as Page Number: 548 the degrees of freedom increase.
Power lines and cancer Does living near power lines cause leukemia in
children? The National Cancer Institute spent years and million gathering data on this question. The researchers compared children who had leukemia with who did not. They went into the homes and measured the magnetic fields in children鈥檚 bedrooms, in other rooms, and at the front door. They recorded facts about power lines near the family home and also near the mother鈥檚 residence when she was pregnant. Result: No association between leukemia and exposure to magnetic fields of the kind produced by power lines was found.
a. Was this an observational study or an experiment? Justify your answer.
b. Does this study prove that living near power lines doesn鈥檛 cause cancer? Explain your answer.
How confident? The figure shows the result of taking SRSs from a Normal population and constructing a confidence interval for the population mean using each sample. Which confidence level鈥�鈥攄o you think was used? Explain your reasoning.
Travel time to work A study of commuting times reports the travel times to work of a random sample of employed adults in New York State. The mean is minutes and the standard deviation is
minutes. What is the standard error of the mean? Interpret this value in context.
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