18. A company distributes cola in cans labeled 12 ounces. A government agency thinks that the company is cheating its customers. Assume that if a company's average can contains 12 ounces, then the company is not cheating. The agency selects 50 random cans, measures their contents, and obtains a sample mean of 11.9 ounces with a population standard deviation of 0.40 ounce. a) The sample mean is 11.9. Before doing any work, what is gut feeling about the chances of the population mean being less than or equal to 12? Do you think that the sample mean of 11.9 is low enough and provides enough evidence?

b) Which will you use to perform the hypothesis test, a z-test or t-test? Explain why.

c) At = 0.01, test the agency's claim. d) Complete the hypothesis test and compare with your guess in part a.