Cigarette Tar The mean tar content of a simple random sample of 25 unfiltered king-size cigarettes is 21.1 mg, with a standard deviation of 3.2 mg. The mean tar content of a simple random sample of 25 filtered 100-mm cigarettes is 13.2 mg with a standard deviation of 3.7 mg

(from Data Set 15 “Cigarette Contents” in Appendix B).

a. Use a 0.05 significance level to test the claim that unfiltered king-size cigarettes have a mean tar content greater than that of filtered 100-mm cigarettes. What does the result suggest about the effectiveness of cigarette filters?

b. Construct a 90% confidence interval estimate of the difference between the mean tar content of unfiltered king-size cigarettes and the mean tar content of filtered 100-mm cigarettes. Does the result suggest that 100-mm filtered cigarettes have less tar than unfiltered king-size cigarettes?