Exam 9: Estimation and Confidence Intervals

William S.Gosset,a brewmaster,developed the t test for the Guiness Brewery in Ireland and published it in 1908 using the pen name "Student."

A bank wishes to estimate the mean credit card balance owed by its customers.The population standard deviation is estimated to be $300.If a 98 percent confidence interval is used and an interval of $75 is desired,how many customers should be sampled?

A company wants to estimate next years total revenue.Why is an interval estimate preferred to a point estimate?

Mileage tests were conducted on a randomly selected sample of 100 newly developed automobile tires.The results showed that the average tread life was 50,000 miles with a standard deviation of 3,500 miles.What is the best estimate of the average tread life in miles for the entire population of these tires?

If 95% and 98% confidence intervals were developed to estimate the true cost of the microwave,what differences would they have?

For a given confidence interval,what is the interpretation of a 96% confidence level?

An interval estimate is a single value used to estimate a population parameter.

The Student t distribution has a greater spread than the z distribution.As a result,the critical values of t for a given level of significance are larger than the corresponding z critical values.

The proportion of junior executives leaving large manufacturing companies within three years is to be estimated within 3 percent.The 0.95 degree of confidence is to be used.A study conducted several years ago revealed that the percent of junior executives leaving within three years was 21.To update this study,the files of how many junior executives should be studied?

To determine the value of the standard error of the mean,the total error is divided by the sample size.

A group of statistics students decided to conduct a survey at their university to estimate the average (mean)amount of time students spent studying per week.They sampled 554 students and found a mean of 22.3 hours per week.Assuming a population standard deviation of 6 hours,what is the 95% level of confidence?

A survey of 25 grocery stores revealed that the average 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 t distribution is based on the assumption that the population of interest is normal or nearly normal.

The test statistic for a problem involving any sample size and an unknown population standard deviation is the Student's t distribution.

A distribution of sample means is normally distributed with a mean equal to the population mean and a standard deviation equal to the standard error of the mean.

The mean number of travel days per year for salespeople employed by 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 local retail company wants to estimate the mean amount spent.Their budget limits the number of surveys to 225.What is their maximum error of the estimated mean amount spent for a 99% level of confidence and an estimated standard deviation of $10.00?

When we use a confidence interval to reach a conclusion about the population mean,we are applying a type of reasoning or logic called

When a confidence interval for a population mean is constructed from sample data,

A survey of an urban university (population of 25,450)showed that 870 of 1100 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?