Awater tank holds 18000 gallons. how long will it take for the water level to reach 6000 gallons if the water is used at an average rate of 450 gallons per day?

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”?