13. The grades of the students in a large statistics class are normally distributed around a mean of 70, with a standard deviation of 5. If the instructor decides to give an "A" grade only to the top 15% of the class, what grade must a student earn to be awarded an A? 14. Suppose the instructor in the class in problem 13 decided to give an "A" grade only to the top 10% of the class. What grade would the student now have to earn to be awarded ah A?