Compute a 95% confidence interval for the population mean, based on the sample numbers 21, 28, 33, 34, 25, 26, and 135. Which table do we use to find...

1. Compute a 95% confidence interval for the population mean, based on the sample numbers 21, 28, 33, 34, 25, 26, and 135.

Which table do we use to find the margin of error?

2. The report of a sample survey of 1014 adults says, "with 95% confidence, between 9% and 15% of all Americans expect to spend more on gifts this year than last year."

What does the phrase "95% confidence" mean?

A. The method used to get the interval 9% to 15%, when used over and over again, produces intervals which include the true population proportion 95% of the time.

B. 95% of all Americans will spend between 9% and 15% more than what they spent last year.

C. 9% to 15% of all Americans will spend 95% of what they spent last year.

D. There is a 95% chance that the percent who expect to spend more is between 9% and 15%.

3. What is the critical value of t for a 90% confidence interval with df = 14? (Assume a 2-tailed test)

4. What is the critical value for a 95% confidence interval based on a sample size of 20? (Population standard deviation is unknown). (Assume a 2-tailed test)