The sum of 4 times mike's age and 3 times susan's age is 79. mike is 1 year more than 3 times as old as susan. find each of their ages.

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”?