1.What is a 90 percent confidence interval for the population mean when the sample size equals 12, the sample mean equals 35.6, and the sample standard deviation equals 13.3? Assume the population is normally distributed.

2.Use the following values for x (the independent variable) and y (the dependent variable) to perform a regression analysis. Find the 90 percent confidence interval for the slope.

x = 39, 38, 15, 13, 10

y = 59, 59, 29, 19, 14

3.Given the following data, find a 90 percent confidence interval for the average value of y when x equals 20.

x = 10, 12, 13, 20, 21, 22, 22, 24, 26

y = 19, 19, 18, 19, 16, 12, 13, 11, 11

4.National Motor Company claims that one of its models, the Econo, gets city driving mileages that are normally distributed with a population mean of 30 miles per gallon and a population standard deviation of 3 miles per gallon. If one of the Econo models is randomly selected and if National Motor Company's claim is true, what is the probability that the automobile will get 22 miles per gallon or more?