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complete exercises 9.3, 9.13, 9.14, 9.25, 9.48, 9.55




Complete exercises 9.3, 9.13, 9.14, 9.25, 9.48, 9.55



9.3 If you use a 0.10 level of significance in a two-tail


hypothesis test, what is your decision rule for rejecting a


null hypothesis that the population mean is 500 if you use


the Z test?



9.13 Do students at your school study more than, less


than, or about the same as students at other business


schools? BusinessWeek reported that at the top 50 business


schools, students studied an average of 14.6 hours per


week. (Data extracted from “Cracking the Books,” Special


Report/Online Extra,, March 19,


2007.) Set up a hypothesis test to try to prove that the


mean number of hours studied at your school is different


from the 14.6-hour-per-week benchmark reported by




a. State the null and alternative hypotheses.


b. What is a Type I error for your test?


c. What is a Type II error for your test?




9.14 The quality-control manager at a light bulb


factory needs to determine whether the mean life of


a large shipment of light bulbs is equal to 375 hours. The population


standard deviation is 100 hours. A random sample of


64 light bulbs indicates a sample mean life of 350 hours.


a. At the 0.05 level of significance, is there evidence that


the mean life is different from 375 hours?


b. Compute the p-value and interpret its meaning.


c. Construct a 95% confidence interval estimate of the population


mean life of the light bulbs.


d. Compare the results of (a) and (c). What conclusions do


you reach?



9.25 A manufacturer of chocolate candies uses machines


to package candies as they move along a filling line. Although


the packages are labeled as 8 ounces, the company


wants the packages to contain a mean of 8.17 ounces so that


virtually none of the packages contain less than 8 ounces. A


sample of 50 packages is selected periodically, and the


packaging process is stopped if there is evidence that the


mean amount packaged is different from 8.17 ounces. Suppose


that in a particular sample of 50 packages, the mean


amount dispensed is 8.159 ounces, with a sample standard


deviation of 0.051 ounce.


a. Is there evidence that the population mean amount is


different from 8.17 ounces? (Use a 0.05 level of




b. Determine the p-value and interpret its meaning.



9.48 Southside Hospital in Bay Shore, New York,


commonly conducts stress tests to study the heart


muscle after a person has a heart attack. Members of the diagnostic


imaging department conducted a quality improvement


project with the objective of reducing the turnaround time for


stress tests. Turnaround time is defined as the time from when


a test is ordered to when the radiologist signs off on the test


results. Initially, the mean turnaround time for a stress test was


68 hours. After incorporating changes into the stress-test


process, the quality improvement team collected a sample of


50 turnaround times. In this sample, the mean turnaround


time was 32 hours, with a standard deviation of 9 hours. (Data


extracted from E. Godin, D. Raven, C. Sweetapple, and


F. R. Del Guidice, “Faster Test Results,” Quality Progress,


January 2004, 37(1), pp. 33–39.)


a. If you test the null hypothesis at the 0.01 level of significance,


is there evidence that the new process has reduced


turnaround time?


b. Interpret the meaning of the p-value in this problem.



9.55 The U.S. Department of Education reports that 46%


of full-time college students are employed while attending


college. (Data extracted from “The Condition of Education


2009,” National Center for Education Statistics, nces.ed.


gov.) A recent survey of 60 full-time students at Miami University


found that 29 were employed.


a. Use the five-step p-value approach to hypothesis testing


and a 0.05 level of significance to determine whether the


proportion of full-time students at Miami University is


different from the national norm of 0.46.


b. Assume that the study found that 36 of the 60 full-time


students were employed and repeat (a). Are the conclusions


the same?





For problems requiring computations, please ensure that your Excel file includes the associated cell computations and/or statistics output; this information is needed in order to receive full credit on these problems.


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