Exam 8: Estimating Single Population Parameters

A hospital emergency room has collected a sample of n = 40 to estimate the mean number of visits per day.It has found the standard deviation is 32.Using a 90 percent confidence level,what is its margin of error?

The following data represent a random sample of bank balances for a population of checking account customers at a large eastern bank.Based on these data,what is the 95 percent confidence interval estimate for the true population mean?

Which of the following statements is true with respect to the t-distribution?

The one sure thing that can be said about a point estimate is that it will most likely be subject to sampling error and not equal the parameter.

A report in a consumer magazine indicated that with 90 percent confidence,the mean number of hours that a particular brand light bulb lasts is between 900 and 1,100 hours.Based on this,the sample mean that produced this estimate is 1,000 hours.

All other factors held constant,the higher the confidence level,the closer the point estimate for the population mean will be to the true population mean.

A bank manager wishes to estimate the mean waiting time spent by customers at his bank.He knows from previous experience that the standard deviation is about 4.0 minutes.If he desires a 90 percent confidence interval estimate and wishes to have a margin of error of 1 minute,the required sample size will be approximately 143.

A local pizza company is interested in estimating the percentage of customers who would take advantage of a coupon offer.To do this,they give the coupon out to a random sample of 100 customers.Of these,45 actually use the coupon.At the 95 percent confidence level it would be appropriate for the manager to conclude that possibly as many as 50 percent of his customers will redeem the coupon.

The impact on the margin of error for a confidence interval for an increase in confidence level and a decrease in sample size is unknown since these changes are contradictory.

The higher the level of confidence,the wider the confidence interval must be.

In estimating a population mean,under what conditions would the t-distribution be used?

In determining the required sample size in an application involving an estimate for the population mean,if the population standard deviation is known,there is no compelling reason to select a pilot sample.

The bottlers of a new fruit juice daily select a random sample of 12 bottles of the drink to estimate the mean quantity of juice in the bottles filled that day.On one such day,the following results were observed: = 12.03; s = 0.12.Based on this information,the upper limit for a 95 percent confidence interval estimate is approximately 12.106 ounces.

When determining sample size for a proportion,the farther that π is from 0.5,the smaller the resulting sample size will be.

A human resources manager wishes to estimate the proportion of employees in her large company who have supplemental health insurance.What is the largest size sample she should select if she wants 95 percent confidence and a margin of error of ± 0.01?

In an application to estimate the mean number of miles that downtown employees commute to work roundtrip each day,the following information is given: Based on this information,the upper limit for a 95 percent confidence interval estimate for the true population mean is:

A grocery store manager is interested in estimating the mean weight of apples received in a shipment.If she wishes to have the estimate be within ± .05 pound with 90 percent confidence,the sample size should be 103 apples if she believes that the standard deviation is .08 pounds.

A 95 percent confidence interval for a mean will contain 95 percent of the population within the interval.

A 95 percent confidence interval estimate will have a margin of error that is approximately ± 95 percent of the size of the population mean.

When calculating a confidence interval,the reason for using the t-distribution rather than the normal distribution for the critical value is that the population standard deviation is unknown.