Exam 8: Statistical Inference: Estimation for Single Populations

A large trucking company wants to estimate the proportion of its tracker truck population with refrigerated carrier capacity..A random sample of 200 tracker trucks is taken and 30% of the sample have refrigerated carrier capacity. The 95% confidence interval to estimate the population proportion is _______.

In estimating the sample size necessary to estimate a population mean,the error of estimation,E,is equal to the difference between the sample mean and the sample standard deviation.

The table t value associated with the upper 10% of the t distribution and 23 degrees of freedom 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 95% confidence interval for the population proportion is _________.

An insurance company is interested in conducting a study to to estimate the population proportion of teenagers who obtain a driving permit within 1 year of their 16^th birthday.A level of confidence of 99% will be used and an error of no more than .04 is desired.There is no knowledge as to what the population proportion will be.The size of sample should be at least _______.

A researcher wants to estimate the proportion of the population which possesses a given characteristic.A random sample of size 800 is taken resulting in 360 items which possess the characteristic.The point estimate for this population proportion is _______.

In order to find values in the t distribution table,you must determine the appropriate degrees of freedom based on the sample sizes.

Velma Vasquez,fund manager of the Vasquez Value Fund,manages a portfolio of 250 common stocks. Velma relies on various statistics,such as variance,to assess the overall risk of stocks in an economic sector.Her staff reported that for a sample 14 utility stocks the mean annualized return was 14% and that the variance was 3%. Assume that annualized returns are normally distributed. The 95% confidence interval for the population variance of annualized returns 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.

A researcher wants to estimate the proportion of Millennials who regularly listen to podcasts (defined as at least two entire podcasts per week).Previous studies indicate that only 18% of Millennials listen regularly to podcasts,and this researcher wants to estimate if that figure has increased.For this purpose,the researcher will use a 98% confidence level and wants to estimate the population proportion within 0.01 (i.e.,1 percentage point)of the actual value.The required sample size is at least ______.

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

A researcher wants to estimate the proportion of the manufacturing companies that use the six sigma method.For this purpose,she will take a random sample of 50 manufacturing companies and find out how many of them use this method.She estimates that the proportion will be anywhere from 0.4 to 0.55.Of all these proportions,which one would produce the narrowest 95% confidence interval for the population proportion?

A researcher wants to determine the sample size necessary to adequately conduct a study to estimate the population mean to within 5 points.The range of population values is 80 and the researcher plans to use a 90% level of confidence.The sample size should be at least _______.

If you need to estimate the population mean within 2.5 units and with a confidence level of 95%.The minimum value observed is 15 and the maximum,65.What sample size would you use?

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 ________.

A t-distribution is similar to a normal distribution,but with flatter tails.

The employees of Cybertronics Inc.need to complete a certification online.A random sample of 16 employees gives an average time for completion of all the coursework and passing the tests of 20 hours.The population standard deviation is unknown but the sample standard deviation is 6 hours.You can assume that the population of employees is fairly large.Construct a 95% confidence interval for the average time required to complete the certification.

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 ____.

A researcher wants to estimate the percent of the population that uses the radio to stay informed on local news issues.The researcher wants to estimate the population proportion with a 95% level of confidence. He estimates from previous studies that no more than 30% of the population stay informed on local issues through the radio. The researcher wants the estimate to have an error of no more than .03. The necessary sample size is at least _______.

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 _______.