200 student from each of two different courses sat the same exam (i.e. a total of 400 students). The 200 students in course A scored a mean grade of 68 with a standard deviation of 20, while those in course B had a mean score of 73 with a standard deviation of 18. Is there any reason to believe that students in course B are significantly better than those in course A? Use the 5% significance level.