Question: A sample of 15 students enrolled in an economics class had the following scores on the first exam: 60, 75, 80, 70, 90, 78, 84, 97, 81, 77, 69, 88, 91, 75, and 68. Assume the population of scores is normally distributed. Find 98%, 95.5%, and 93.5% confidence interval estimates for the population mean grade of all students taking the first exam in that course.