Suppose a normal model has a standard deviation of sigmaσequals=10, and 60% of the values are below 75. Which of the following must be true about the mean? a. The mean must be less than 75 B. the mean must be greater than 75 c. the mean must be equal to 75 d. not enough info to tell anythng about mean A. The mean must be less than 75. B. The mean must be greater than 75. C. The mean must be equal to 75. D. There is not enough information to determine anything about the mean. A. The mean must be less than 75. B. The mean must be greater than 75. C. The mean must be equal to 75. D. There is not enough information to determine anything about the mean. A. The mean must be less than 75. B. The mean must be greater than 75. C. The mean must be equal to 75. D. There is not enough information to determine anything about the mean.