4. Past experience indicates that the time required for the students in Prob & Stat class to complete the final exam is normally distributed with a mean of 115 minutes. If a random sample of 20 students in the class took an average of 105.3 minutes to complete the final exam with a standard deviation of 14.7 minutes, test the hypothesis, at the 0.05 level of significance, that / = 115 minutes against the alternative that u