Exam 8: Interval Estimation

A sample of 144 cans of coffee showed an average weight of 16 ounces.The standard deviation of the population is known to be 1.4 ounces. a.Construct a 68.26% confidence interval for the mean of the population. b.Construct a 97% confidence interval for the mean of the population. c.Discuss why the answers in Parts a and b are different.

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.

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 95% confidence interval for the average hourly wage of all information system managers is

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.

The value added and subtracted from a point estimate in order to develop an interval estimate of the population parameter is known as the

A random sample of 144 observations has a mean of 20,a median of 21,and a mode of 22.The population standard deviation is known to equal 4.8.The 95.44% confidence interval for the population mean is

In order to use the normal distribution for interval estimation of $\mu$ when $\sigma$ is known and the sample is very small,the population

The following random sample from a population whose values were normally distributed was collected. The 95% confidence interval for $\mu$ is

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

A coal company wants to determine a 95% confidence interval estimate for the average daily tonnage of coal that they mine.Assuming that the company reports that the standard deviation of daily output is 200 tons,how many days should they sample so that the margin of error will be 39.2 tons or less?

Below you are given ages that were obtained by taking a random sample of 9 undergraduate students.Assume the population has a normal distribution. a.What is the point estimate of $\mu$ ? b.Determine the standard deviation. c.Construct a 90% confidence interval for the average age of undergraduate students. d.Construct a 99% confidence interval for the average age of undergraduate students. e.Discuss why the 99% and 90% confidence intervals are different.

In a random sample of 100 observations, = 0)2.The 95.44% confidence interval for P is

After computing a confidence interval,the user believes the results are meaningless because the width of the interval is too large.Which one of the following is the best recommendation?

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 random sample of 6 observations.Assume the population has a normal distribution. a.What is the point estimate of $\mu$ ? b.Construct an 80% confidence interval for $\mu$ . c.Construct a 98% confidence interval for $\mu$ . d.Discuss why the 80% and 98% confidence intervals are different.

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.If we want to determine a 95% confidence interval for the average hourly income,the value of "t" statistics is

From a population that is normally distributed,a sample of 25 elements is selected and the standard deviation of the sample is computed.For the interval estimation of $\mu$ ,the proper distribution to use is the

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.If the sample mean is 1,858 KWH,the 95% confidence interval estimate of the population mean is

A sample of 200 elements from a population with a known standard deviation is selected.For an interval estimation of $\mu$ ,the proper distribution to use is the

Two hundred students are enrolled in an Economics class.After the first examination,a random sample of 6 papers was selected.The grades were 65,75,89,71,70 and 80. a.Determine the standard error of the mean. b.What assumption must be made before we can determine an interval for the mean grade of all the students in the class? Explain why. c.Assume the assumption of Part b is met.Provide a 95% confidence interval for the mean grade of all the students in the class.