A, B, C are the three collinear points such that AB=BC. If the coordinate of A, B, and C are (a, 2), (1, 3), (5, b) respectively. Find a and b

Scores on a university exam are normally distributed with a mean of 78 and a standard deviation of 8. the professor teaching the class declares that a score of 70 or higher is required for a grade of at least “c.” using the 68-95-99.7 rule, what percentage of students failed to earn a grade of at least “c”?