EX 1EX 1

A personnel manager has found that, historically, A personnel manager has found that, historically, the scores on aptitude tests given to applicants for the scores on aptitude tests given to applicants for entry level positions follow a normal distribution entry level positions follow a normal distribution with standard deviation of 32.4 points a random with standard deviation of 32.4 points a random sample of 9 test scores from the current group of sample of 9 test scores from the current group of applicants had a mean score of 187.9 points.applicants had a mean score of 187.9 points.

a. Find the 90% confidence interval for the a. Find the 90% confidence interval for the population mean score of the current group of population mean score of the current group of applicants.applicants.

b. Based on these sample results, a statistician b. Based on these sample results, a statistician found for the population mean, a confidence interval found for the population mean, a confidence interval extending from 165.8 to 210.0 points. Find the extending from 165.8 to 210.0 points. Find the confidence level for this interval.confidence level for this interval.

EX 2EX 2

There is a concern about speed of There is a concern about speed of automobiles travelling over a particular automobiles travelling over a particular

stretch of highway. For a random stretch of highway. For a random sample of 7 automobiles, radar sample of 7 automobiles, radar

indicated the following speeds in miles indicated the following speeds in miles per hour. per hour.

79 73 79 73 6868 7777 8686 7171 6969

Assuming a normal population distribution Assuming a normal population distribution find the marginal error of a 95% find the marginal error of a 95%

confidence interval for the mean speed confidence interval for the mean speed of all automobiles travelling over the of all automobiles travelling over the

stretch of highway.stretch of highway.

EX 3EX 3Suppose that a random sample of a Suppose that a random sample of a 600 registered voters in one Florida 600 registered voters in one Florida

county, 87.9% strongly agreed with the county, 87.9% strongly agreed with the statement “the state of Florida should statement “the state of Florida should have only one method of reading and have only one method of reading and

counting ballots” based on this counting ballots” based on this information, you calculated the information, you calculated the

confidence interval for the percentage confidence interval for the percentage of all registered voters.of all registered voters.

EX 4EX 4

A company sends a random sample of 12 of its A company sends a random sample of 12 of its sales people to a course designed to increase sales people to a course designed to increase their motivation and hence presumably, their their motivation and hence presumably, their

effectiveness in the foollowing year, these effectiveness in the foollowing year, these people generated sales with an average value people generated sales with an average value of $435,000 and a sample standard deviation of $435,000 and a sample standard deviation

of $56,000. During the same period, an of $56,000. During the same period, an independently chosen random sample of 15 independently chosen random sample of 15

sales people who had not attended the course sales people who had not attended the course obtained sales with an average value of obtained sales with an average value of

$408,000 and standard deviation $43,000. $408,000 and standard deviation $43,000. Assume that, the two population distributions Assume that, the two population distributions are normal and have the same variance. Find are normal and have the same variance. Find the 95% confidence interval for the difference the 95% confidence interval for the difference

b etween their means.b etween their means.