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a study of 25 drivers showed that they drive an average of 300 miles a week...

a study of 25 drivers showed that they drive an average of 300 miles a week with a standard deviation of 20 miles. Identify the distribution used (t or z) and find and interpret a 95% confident interval for the average number of miles all drivers drive in 1 week. 2. A study of 50 students at a college showed that the average age was 20.2 with a standard deviation of 1.8. Identify the distribution used (t or z) and find and interpret a 99% confidence interval for the average age of all students at the college. 3. If the person running the study in problem 2 wanted the margins of error to be more than .5 years, how many MORE people would need to be sampled? (assume you are staying with a 99% confidence interval) Show work to support answer. 4. you wish to find out how many students at your college take history courses. how many people must you surgery if you wish to be 95% confidents with an error of no more than +- 3%. show work to support answer.

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a study of 25 drivers showed that they drive an average of 300 miles a week with a standard deviation of 20 miles. Identify the distribution used (t or z) and find and interpret a 95% confident interval for the average number of miles all drivers drive in 1 week.

n=25

xbar=300

s=20

df=n-1=25-1=24

alpha/2=0.05/2=0.025

=T.INV(0.025;24)

=2.0639

95% confident interval for the average number of miles all drivers drive in 1 week.

xbar-t*s/sqrt(n),xbar+t*s/sqrt(n)

300-2.0639*20/sqrt(25),300+2.0639*20/sqrt(25)

291.744,308.2556

lower limit=291.744

upper limit=308.256

we are 95% confident interval that the average number of miles all drivers drive in 1 week lies in between 291.744 and 308.256

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