Exam 8: Interval Estimation

From a population that is not normally distributed and whose standard deviation is not known, a sample of 6 items is selected to develop an interval estimate for the mean of the population ( $\mu$ ).

Exhibit 8-4 In order to estimate the average electric usage per month, a sample of 81 houses was selected, and the electric usage was determined. Assume a population standard deviation of 450-kilowatt hours. -Refer to Exhibit 8-4. The standard error of the mean is

A random sample of 121 checking accounts at a bank showed an average daily balance of $300 and a standard deviation of $44. Develop a 95% confidence interval estimate for the mean of the population.

Choo Choo Paper Company produces papers of various thickness. A random sample of 256 cuts had a mean thickness of 30.3 mils with a standard deviation of 4 mils. Develop a 95% confidence interval for the mean thickness of the population.

Six hundred consumers were asked whether they would like to purchase a domestic or a foreign automobile. Their responses are given below. Develop a 95% confidence interval for the proportion of all consumers who prefer to purchase domestic automobiles.

If we want to provide a 95% confidence interval for the mean of a population, the confidence coefficient is

A simple random sample of 36 items resulted in a sample mean of 40 and a standard deviation of 12. Construct a 95% confidence interval for the population mean.

Exhibit 8-6 A sample of 75 information system managers had an average hourly income of $40.75 with a standard deviation of $7.00. -Refer to Exhibit 8-6. The standard error of the mean is

In order to estimate the average electric usage per month, a sample of 196 houses was selected, and their electric usage determined. a.Assume a population standard deviation of 350-kilowatt hours. Determine the standard error of the mean. b.With a 0.95 probability, determine the margin of error. c.If the sample mean is 2,000 KWH, what is the 95% confidence interval estimate of the population mean?

You are given the following information obtained from a random sample of 5 observations taken from a large population. Construct a 95% confidence interval for the mean of the population, assuming the population has a normal distribution.

The ability of an interval estimate to contain the value of the population parameter is described by the

If the population standard deviation of the lifetime of washing machines is estimated to be 900 hours, how large a sample must be taken in order to be 97% confident that the margin of error will not exceed 100 hours?

The monthly incomes from a random sample of workers in a factory are shown below. a.Compute the standard error of the mean (in dollars). b.Compute the margin of error (in dollars) at 95% confidence. c.Compute a 95% confidence interval for the mean of the population. Assume the population has a normal distribution. Give your answer in dollars.

An Excel printout of the descriptive measures of daily checking account balances (in dollars) of customers of First Daisy Bank is shown below. Develop a 95% confidence interval estimate for the mean of the population of the checking balances.

In a random sample of 400 registered voters, 120 indicated they plan to vote for Candidate A. Determine a 95% confidence interval for the proportion of all the registered voters who will vote for Candidate A.

Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.8 hours. -Refer to Exhibit 8-1. The standard error of the mean is

Many people who bought X-Game gaming systems over the holidays have complained that the systems they purchased were defective. In a sample of 1200 units sold, 18 units were defective. a.Determine a 95% confidence interval for the percentage of defective systems. b.If 1.5 million X-Games were sold over the holidays, determine an interval for the number of defectives in sales.

You are given the following information obtained from a sample of 5 observations taken from a population that has a normal distribution. Develop a 98% confidence interval estimate for the mean of the population.

A statistician selected a sample of 16 accounts receivable and determined the mean of the sample to be $5,000 with a standard deviation of $400. He reported that the sample information indicated the mean of the population ranges from $4,739.80 to $5,260.20. He neglected to report what confidence coefficient he had used. Based on the above information, determine the confidence coefficient that was used. Assume the population has a normal distribution.

The proprietor of a boutique in New York wanted to determine the average age of his customers. A random sample of 53 customers revealed an average age of 28 years with a standard deviation of 4 years. Determine a 98% confidence interval estimate for the average age of all his customers.