A cold medicine lists 600 milligrams of acetaminophen per fluid ounce as an active ingredient. A test of 55 one-ounce samples of the medicine finds that the mean amount of acetaminophen for the sample is 592 milligrams with a standard deviation of 21 milligrams. Test the claim that the medicine does not contain the required amount of acetaminophen. Use a 0.05 significance level.