A math instructor has written a new placement exam. He is concerned that the exam may be too long. The instructor claims that the average length of time required to finish the exam for all students who take it is at most 50 minutes. The exam is given to 20 randomly selected students, and their average length of time required to finish the exam was 54 minutes, with a standard deviation of 5.99 minutes. Test the instructor's claim at the 0.05 level of significance.