As a student, you are suspicious that some teachers give easier tests than others. You have heard that Mr. Wilson is one such teacher, and you are thinking of switching to his class. However, you want to be sure that Mr. Wilson's tests are easier. Ms. Hardy has told you that the class average on the first test of the semester was 58.2%. Mr. Wilson did not give out the class average, so you conduct a random sample of 20 students from his class, and get an average mark of 65.4%, with a standard deviation of 18.6. At the 5% level of significance, does this provide evidence that the average mark was higher in Mr. Wilson's class? If so, does this mean that Mr. Wilson's test was easier than Ms. Hardy's? What other explanations should you consider? You may assume the test marks are normally distributed.