3.97 The test scores for a large statistics class have an unknown dis- tribution with a mean of 70 and a standard deviation of 10. a. Find k so that at least 50% of the scores are within k standard deviations of the mean. b. Find k so that at most 10% of the scores are more than k stand- ard deviations above the mean. 3.98 The test scores for a large statistics class have a bell-shaped dis- tribution with a mean of 70 points. a. If 16% of all students in the class scored above 85, what is the standard deviation of the scores? b. If 95% of the scores are between 60 and 80, what is the stand- ard deviation?