Exam 7: Statistical Inference: Estimating a Population Mean

In a random sample of 12 calls made from the U.S.to Japan by callers using Skype during the past week, the average call lasted 21.4 minutes, with a sample standard deviation of 5.1 minutes.Assume the population distribution of call times is normal.Build a 99% confidence interval estimate of the average call time for the population of calls represented by the sample (that is, the population of all calls made from the US to Japan last week by callers using Skype).Report the upper bound for your interval.

Crawford Retailing has 6 sales reps, designated as rep D, E, F, G, H, and I.You will select a simple random sample of these reps.List all the possible samples of size 5.

Which of the following is a NOT a property of the t distribution?

In order to qualify as a source of random numbers, all of the digits that appear in a random number table must be equally represented and must show no pattern to the way they appear in the table.

__________ is a sampling method that ensures that every combination of n members of a population has an equal chance of being selected.

Crownfashions.com wants to estimate the average time that visitors to its website spend browsing the site.In a random sample of 49 visits this week, average browsing time is 13.6 minutes.Assume you know the population standard deviation is 5.2 minutes.Construct an 80% confidence interval estimate of average browsing time for the population of crownfashion.com visitors this week.Report the upper bound for your interval.

Educational Research plans a study to estimate the length of the average workweek for faculty members at public universities by taking a simple random sample of this group.If you want to insure a 90% probability that the sample mean you produce will be no more than 1 hour away from the actual population mean, how large a sample should you select for your study.Based on previous experience, you estimate a population standard deviation of approximately 12 hours.

A simple random sample of size n from a population of size N is to be selected.Each possible sample should have:

In a study of monthly household expenditures for California households, a UCLA research team selected a random sample of 1049 households.Average household expenditure for the sample during the month of April was $2,754, with a sample standard deviation of $243.Show the 99% confidence interval estimate of average April household expenditures for the population California households.Report the upper bound for your interval.

What is the margin of error?

The sampling error is the:

Which of the following is the amount that is added to or subtracted from the sample mean to construct an interval estimate of the population mean?

To determine the proportion of students on campus who would be interested in having coin operated snack machines installed in the Bellarmine dormitory basement, I send out a simple yes or no poll to all Bellarmine dormitory residents.What sampling method am I using?

Simple random sampling is a sampling method which ensures that every combination of n members of the population has an equal chance of being selected.

Using the t table, determine the proper boundaries for an 80% interval (symmetric about the center) for a t distribution with df = 9.Report the upper bound.

The National Center for Health Statistics reports that the average weight in a sample of U.S.men aged 20 to 74 is 191 pounds.If the sample size is 1200 and the population standard deviation is 18.2 pounds, the standard error of the sampling distribution of the sample mean weight is:

Which of the following is NOT a property of the sampling distribution of the sample mean?

The degrees of freedom in the t distribution represents the number of "independent" terms involved in the sample standard deviation calculation.

The standard error is the amount added to and subtracted from the sample mean to obtain an interval estimate of the population mean.

The difference between the mean of any given sample and the mean of the population is called the: