Exam 8: Statistical Inference: Estimation for Single Populations

Brian Vanecek,VP of Operations at Portland Trust Bank,is evaluating the service level provided to walk-in customers.Accordingly,his staff recorded the waiting times for 45 randomly selected walk-in customers,and calculated that their mean waiting time was 15 minutes.If Brian concludes that the average waiting time for all walk-in customers is 15 minutes,he is using a ________.

When the population standard deviation,,is unknown the sample standard deviation,s,is used in determining the interval estimate for the population mean.

Given n = 17,s² = 18.56,and that the population is normally distributed,the 80% confidence interval for the population variance is ________.

In determining the interval estimates for a population variance using the sample variance,it is appropriate to use the values from a chi-square distribution rather than a t-distribution.

The table t value associated with the upper 5% of the t distribution and 14 degrees of freedom is _______.

Suppose a researcher is interested in understanding the variation in the price of store brand milk.A random sample of 36 grocery stores selected from a population and the mean price of store brand milk is calculated.The sample mean is $3.13 with a standard deviation of $0.23.Construct a 95% confidence interval to estimate the population mean.

Brian Vanecek,VP of Operations at Portland Trust Bank,is evaluating the service level provided to walk-in customers.Brian would like to minimize the variance of waiting time for these customers,since this would mean each customer received the same level of service.Accordingly,his staff recorded the waiting times for 15 randomly selected walk-in customers,and determined that their mean waiting time was 15 minutes and that the standard deviation was 4 minutes.Assume that waiting time is normally distributed.The 95% confidence interval for the population variance of waiting times is ________.

Elwin Osbourne,CIO at GFS,Inc.,is studying employee use of GFS e-mail for non-business communications.A random sample of 200 e-mail messages was selected.Thirty of the messages were not business related.The point estimate for this population proportion is _______.

Given the error we are willing to tolerate,the sample size is determined by the meanµ of the population and the confidence level.

The table t value associated with the upper 10% of the t distribution and 23 degrees of freedom is _______.

Given n = 12,s² = 44.90,and that the population is normally distributed,the 99% confidence interval for the population variance is ________.

A study is going to be conducted in which a mean of a lifetime of batteries produced by a certain method will be estimated using a 90% confidence interval.The estimate needs to be within +/- 2 hours of the actual population mean.The population standard deviation is estimated to be around 25.The necessary sample size should be at least _______.

Catherine Chao,Director of Marketing Research,is evaluating consumer acceptance of a new toothpaste package.She plans to use a 95% confidence interval estimate of the proportion of households which prefer the new packages; she will accept a 0.05 error.Previous studies indicate that new packaging has an approximately 70% acceptance rate.The sample size should be at least _______.

A random sample of 225 items from a population results in 60% possessing a given characteristic.Using this information,the researcher constructs a 90% confidence interval to estimate the population proportion.The resulting confidence interval is _______.

Eugene Gates,Marketing Director of Mansfield Motors Manufacturers,Inc.'s Electrical Division,is leading a study to assess the relative importance of product features.An item on a survey questionnaire distributed to 100 of Mansfield's customers asked them to rate the importance of "ease of maintenance" on a scale of 1 to 10 (with 1 meaning "not important" and 10 meaning "highly important").His staff assembled the following statistics. If Eugene concludes that the average rate of "ease of maintenance" for all customers is 7.5,he is using ________.

The z value associated with a two?sided 95% confidence interval is _______.

A large national company is considering negotiating cellular phone rates for its employees.The Human Resource department would like to estimate the proportion of its employee population who own an Apple iPhone.A random sample of size 250 is taken and 40% of the sample own and iPhone..The 95% confidence interval to estimate the population proportion is _______.

If the population is not normal but its standard deviation, is known and the sample size,n is large (n ≥ 30),z-distribution values may be used to determine interval estimates for the population mean.

A large national company is considering negotiating cellular phone rates for its employees.The Human Resource department would like to estimate the proportion of its employee population who own an Apple iPhone..A random sample of size 250 is taken and 40% of the sample own and iPhone.The 90% confidence interval to estimate the population proportion is ____.

Suppose a researcher is interested in understanding the variation in the price of store brand milk.A random sample of 36 grocery stores selected from a population and the mean price of store brand milk is calculated.The sample mean is $3.13 with a standard deviation of $0.23.Construct a 99% confidence interval to estimate the population mean..