Exam 9: Estimation and Confidence Intervals

Forty-nine items are randomly selected from a population of 200 items. The sample mean is 30 and the sample standard deviation is 16. What is the 99 percent confidence interval for the population mean?

A survey of households in a small town showed that in 500 of 1,200 sampled households, at least one member attended a town meeting during the year. Using the 95% level of confidence, what is the confidence interval for the proportion of households represented at a town meeting?

Increasing sample sizes result in _______________ interval estimates of a population parameter.

A survey of 50 retail stores revealed that the average price of a microwave was $375 with a sample standard deviation of $20. Assuming the population is normally distributed, what is the 99% confidence interval to estimate the true cost of the microwave?

A confidence interval for a population proportion uses the uniform distribution to approximate the binomial distribution.

A survey of an urban university (population of 25,450) showed that 750 of 1,100 students sampled attended a home football game during the season. Using the 90% level of confidence, what is the confidence interval for the proportion of students attending a football game?

Explain the concept of a confidence interval when estimating a population mean.

Which of the following is NOT necessary to determine how large a sample to select from a population?

To calculate the sample size required to estimate a population mean, we must know or estimate the ______________ of the population distribution.

A point estimate is a single value used to estimate a population parameter.

A university wants to determine the proportion of students who use a cash card to pay at the university food service. Out of 100 students surveyed, 65 students use a cash card. Estimate the value of the population proportion.

A survey of an urban university (population of 25,450) showed that 870 of 1,100 students sampled supported a fee increase to fund improvements to the student recreation center. Using the 95% level of confidence, what is the confidence interval for the proportion of students supporting the fee increase?

A local grocery store wants to estimate the mean daily number of gallons of milk sold to customers. Assume the number of gallons sold follows the normal distribution, with a population standard deviation of 5.10 gallons. A random sample of 60 days shows that the mean daily number of gallons sold is 10.00. Compute a 99% confidence interval for the population mean.

The Nile Superstore is conducting a survey of consumer preferences for a new wireless e-book reader. A sample of 160 people reveals that 120 would buy the new reader. Estimate the value of the population proportion.

A survey of 25 grocery stores revealed that the mean price of a gallon of milk was $2.98, with a standard error of $0.10. What is the 95% confidence interval to estimate the true cost of a gallon of milk?

The mean number of travel days per year for salespeople employed by three hardware distributors needs to be estimated with a 0.90 degree of confidence. For a small pilot study, the mean was 150 days and the standard deviation was 14 days. If the population mean is estimated within two days, how many salespeople should be sampled?

A sample standard deviation is the best point estimate of the ___________.

An interval estimate is a range of values used to estimate a population parameter.

Assuming a normal population with a known population standard deviation, the z statistic for a 99% confidence interval would be ______.

A confidence interval becomes narrower when the sample size _________.