A teacher knows that the test score of a student taking his final examination is a random variable with mean 60. Suppose the teacher also knows that the standard deviation of a student's test score is equal to 9. There are 100 students taking the test. a) What can be said about the probability that a student will score between 45 and 75? b) What can be said about the probability that the class average would be within 5 of the mean?