Chapter 9

In a recent Zogby poll of 1,000 adults nationwide, 613 said they believe other forms of life exist elsewhere in the universe. Construct the 99 percent confidence interval for the population proportion of those believing life exists elsewhere in the universe. Does your result imply that a majority of Americans believe life exists outside of Earth?

As part of an annual review of its accounts, a discount brokerage selects a random sample of 36 customers. Their accounts are reviewed for total account valuation. which showed a mean of \(\$ 32,000\), with a sample standard deviation of \(\$ 8,200 .\) What is a 90 percent confidence interval for the mean account valuation of the population of customers?

A sample of 352 subscribers to Wired magazine shows the mean time spent using the Internet is 13.4 hours per week, with a sample standard deviation of 6.8 hours. Find the 95 percent confidence interval for the mean time Wired subscribers spend on the Internet.

The Tennessee Tourism Institute (TTI) plans to sample information center visitors entering the state to learn the fraction of visitors who plan to camp in the state. Current estimates are that 35 percent of visitors are campers. How large a sample would you take to estimate at a 95 percent confidence level the population proportion with an allowable error of 2 percent?