Exam 8: Interval Estimation

If we want to provide a 95% confidence interval for the mean of a population,the confidence coefficient is

A random sample of 81 children with working mothers showed that they were absent from school an average of 6 days per term with a standard deviation of 1.8 days.Provide a 95% confidence interval for the average number of days absent per term for all the children.

A random sample of 81 students at a local university showed that they work an average of 60 hours per month with a standard deviation of 18 hours.Compute a 95% confidence interval for the mean of the population.

In a poll of 600 voters in a campaign to eliminate non-returnable beverage containers,210 of the voters were opposed.Develop a 92% confidence interval estimate for the proportion of all the voters who opposed the container control bill.

Exhibit 8-2 A random sample of 121 automobiles traveling on an interstate showed an average speed of 65 mph.From past information,it is known that the standard deviation of the population is 22 mph. -Refer to Exhibit 8-2.The 96.6% confidence interval for $\mu$ is

A random sample of 49 lunch customers was taken at a restaurant.The average amount of time the customers in the sample stayed in the restaurant was 45 minutes with a standard deviation of 14 minutes. a.Compute the standard error of the mean. b.With a .95 probability,what statement can be made about the size of the margin of error? c.Construct a 95% confidence interval for the true average amount of time customers spent in the restaurant. d.With a .95 probability,how large of a sample would have to be taken to provide a margin of error of 2.5 minutes or less?

Exhibit 8-6 A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. -Refer to Exhibit 8-6.The standard error of the mean is

A researcher is interested in determining the average number of years employees of a company stay with the company.If past information shows a standard deviation of 7 months,what size sample should be taken so that at 95% confidence the margin of error will be 2 months or less?

For the interval estimation of $\mu$ when $\sigma$ is known and the sample is large,the proper distribution to use is

Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university,data were collected for a sample of 81 business students over a one-week period.Assume the population standard deviation is 1.8 hours. -Refer to Exhibit 8-1.With a 0.95 probability,the margin of error is approximately

Exhibit 8-2 A random sample of 121 automobiles traveling on an interstate showed an average speed of 65 mph.From past information,it is known that the standard deviation of the population is 22 mph. -Refer to Exhibit 8-2.The standard error of the mean is

A population has a standard deviation of 50.A random sample of 100 items from this population is selected.The sample mean is determined to be 600.At 95% confidence,the margin of error is

Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university,data were collected for a sample of 81 business students over a one-week period.Assume the population standard deviation is 1.8 hours. -Refer to Exhibit 8-1.If the sample mean is 9 hours,then the 95% confidence interval is

It is known that the variance of a population equals 1296.A random sample of 144 observations is going to be taken from the population. a.With a 0.95 probability,what statement can be made about the size of the margin of error? b.With a 0.95 probability,how large of a sample would have to be taken to provide a margin of error of 6 or less?

A sample of 225 elements from a population with a standard deviation of 75 is selected.The sample mean is 180.The 95% confidence interval for $\mu$ is

A machine that produces a major part for an airplane engine is monitored closely.In the past,10% of the parts produced would be defective.With a .95 probability,the sample size that needs to be taken if the desired margin of error is .04 or less is

Exhibit 8-6 A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. -Refer to Exhibit 8-6.The value of the margin of error at 95% confidence is

A random sample of 49 statistics examinations was taken.The average score,in the sample,was 84 with a variance of 12.25.The 95% confidence interval for the average examination score of the population of the examinations is

It is known that the variance of a population equals 1,936.A random sample of 121 has been taken from the population.There is a .95 probability that the sample mean will provide a margin of error of

A local university administers a comprehensive examination to the recipients of a B.S.degree in Business Administration.A sample of 5 examinations is selected at random and scored.The scores are shown below. a.Compute the sample mean and the standard deviation. b.Determine the margin of error at 95% confidence. c.At 95% confidence,determine an interval for the mean of the population.At 98% confidence,determine an interval for the mean of the population.