The chief chemist for a major oil/gasoline production company claims that the regular unleaded gasoline produced by the company contains on average 4...

The chief chemist for a major oil/gasoline production company claims that the regular unleaded gasoline produced by the company contains on average 4 ounces of a certain ingredient. The chemist further states that the distribution of this ingredient per gallon of regular unleaded gasoline is normal and has a standard deviation of 1.2 ounces. What is the probability of finding an average less than 3.85 ounces of this ingredient from randomly inspected 64 gallons of regular unleaded gasoline?