Exam 8: Interval Estimation

A random sample of 53 observations was taken. The average in the sample was 90 with a variance of 400. a.Construct a 98% confidence interval for $\mu$ . b.Construct a 99% confidence interval for $\mu$ . c.Discuss why the 98% and 99% confidence intervals are different. d.What would you expect to happen to the confidence interval in Part a if the sample size was increased? Be sure to explain your answer.

The absolute value of the difference between the point estimate and the population parameter it estimates is

In a sample of 400 voters, 360 indicated they favor the incumbent governor. The 95% confidence interval of voters not favoring the incumbent is

The monthly starting salaries of students who receive an MBA degree have a population standard deviation of $110. What size sample should be selected to obtain a 0.95 probability of estimating the mean monthly income within $20 or less?

If we change a 95% confidence interval estimate to a 99% confidence interval estimate, we can expect

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.

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.

In an interval estimation for a proportion of a population, the critical value of Z at 99.2% confidence is

When "S" is used to estimate " $\sigma$ ," the margin of error is computed by using

The t value for a 95% confidence interval estimation with 24 degrees of freedom is

Below you are given ages that were obtained by taking a random sample of 9 undergraduate students. Assume the population has a normal distribution. 40 42 43 39 37 39 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.

Which of the following best describes the form of the sampling distribution of the sample proportion?

An estimate of a population parameter that provides an interval of values believed to contain the value of the parameter is known as the

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?

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.

A university planner is interested in determining the percentage of spring semester students who will attend summer school. She takes a pilot sample of 160 spring semester students discovering that 56 will return to summer school. a.Construct a 95% confidence interval estimate for the percentage of spring semester students who will return to summer school. b.Using the results of the pilot study with a 0.95 probability, how large of a sample would have to be taken to provide a margin of error of 3% or less?

A simple random sample of 144 items resulted in a sample mean of 1257.85 and a standard deviation of 480. Develop a 95% confidence interval for the population mean.