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Chapter 8: Q 8.86 (page 333)
Fuel Expenditures. In estimating the mean monthly fuel expenditure, , per household vehicle, the Energy Information ministration takes a sample of size . Assuming that . determine the margin of error in estimating at the level of confidence.
Margin of Error is and confidence level is .
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Explain the effect on the margin of error and hence the effect on the accuracy of estimating a population mean by a sample mean.
Increasing the confidence level while keeping same sample size.
Poverty and Dietary Calcium. Refer to Exercise
a. Determine and interpret a upper confidence bound for the mean calcium intake of all people with incomes below the poverty level.
b. Compare your one-sided confidence interval in part (a) to the (twosided) confidence interval found in Exercise
Big Bucks. In the article "The Club" (The Business Journal, Vol. 24, Issue 14, Pp. 80-82), J. Trunelle et al. examined Arizona public-company executives with salaries and bonuses totaling over The following data provide the salaries, to the nearest thousand dollars, of a random sample of such executives. 
For a curve with , use Table IV to find each value.
a.
b.
c.
Bicycle Commuting Times. A city planner working on bikeways designs a questionnaire to obtain information about local bicycle commuters. One of the questions asks how long it takes the rider to pedal from home to his or her destination. A sample of local bicycle commuters yields the following times, in minutes. 
a. Find a confidence interval for the mean commuting time of all local bicycle commuters in the city. (Note: The sample mean and sample standard deviation of the data are minutes and minutes, respectively.)
b. Interpret your result in part (a).
c. Graphical analyses of the data indicate that the time of utes may be an outlier. Remove this potential outlier and repeat part (a). (Note: The sample mean and sample standard deviation of the abridged data are and , respectively.)
d. Should you have used the procedure that you did in part (a)? Explain your answer.
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