Exam 7: Statistical Inference: Estimating a Population Mean

Using the t table, determine the proper boundaries for a 95% interval (symmetric about the center) for a t distribution with df = 17.Report the upper bound.

Before any order is shipped, inspectors at Alvarez Manufacturing test a sample of finished units for breaking strength.You select a simple random sample of 49 units from a recently completed order and find that the sample average breaking strength is 814 pounds.Assume that the standard deviation of the breaking strengths for the population of units in the order is known to be 35 pounds.Construct a 95% confidence interval estimate of the average breaking strength you could expect to find if all the units in the order were tested.Report the upper bound for your interval.

The margin of error is the minimum difference we would expect between a particular sample mean and the overall population mean at a specified level of confidence.

The number of job offers received by this year's five International Business graduates of Barlow College are shown below: Suppose you were to take all possible simple random samples of size 2 that could be selected from this graduate population and calculated the sample mean number of offers for each sample.Which one of the following tables shows the sampling distribution of the sample mean?

Fifteen freshmen, 15 sophomores, 15 juniors, and 15 seniors of a university were surveyed to study the sleeping habits of college students throughout their college years.The best description of the sampling method used is

Plainfield Telemarketing plans to estimate the average number of telephone contacts made by its 245 sales reps over the past month.A sample of reps will be randomly selected for the estimate.To construct a 99% confidence interval estimate in which the margin of error will be no more than 20 contacts, how many reps should be included in the sample? Assume a similar study showed a standard deviation of 120 contacts.

You want to build a 99% confidence interval estimate of the mean of a large population.You want the margin of error to be no more than 5.You estimate that the population standard deviation is 50.How big a sample should you select?

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

A non-random sampling procedure that involves deliberately, rather than randomly, selecting certain "representative" population members for inclusion in the sample is called:

The law of large numbers establishes that sample means will approach the mean of the parent population as sample size increases.

Which of the following is not a proper method for selecting a random sample?

The table below shows the names of the sales staff at Porter-Waggoner Accounting, together with the number of major accounts that each one services: List all 4 possible samples of size 3 that could be selected from this population, using sampling without replacement.

An example of systematic sampling is when every 20th item on a list of population members is selected for inclusion in the sample.

Chen Inc.wants to estimate the TOTAL processing time for 2000 current orders.You take a simple random sample of 40 orders, and determine the average processing time required for the orders in the sample is 6.5 hours, with a sample standard deviation of 1.6 hours.Build the 95% confidence interval estimate of the TOTAL processing time required for these 2000.Show the upper bound for your interval.

Flagg and Rossi own a fleet of four limos.The current odometer readings for the four limos are shown in the table below: Suppose you were to take all possible simple random samples of size 2 that could be selected from this limo population and calculated the sample mean odometer reading for each sample.Which one of the following graphs shows the sampling distribution of the sample mean?

In a study of the paperwork required to file for a product patent, the US Patent Office selected a random sample of 1500 applicants who applied for a patent during the past five years.The study found the average time applicants in the sample took to fill out the required forms was 28.4 hours, with a sample standard deviation of 5.7 hours.Use sample results to build a 95% confidence interval estimate of the average time taken filling application forms for the population of all patent applicants during this five-year period.Show the upper bound for your interval.

Sampling with replacement is a sampling procedure in which a population member could be included more than once in the sample.

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 4.

When constructing a confidence interval, an increase in sample size will:

You plan to build a 95% confidence interval estimate of the mean of a large population.You want a margin of error no larger than +10.You estimate the population standard deviation to be 200.How large a sample is needed?