The mean or average of the data set would be misleading because there is an outlier, meaning that one of the numbers is either significantly lower or higher than the rest. That can be seen here because of the number 77.
Honestly I couldn't understand most of that but if one gallon of oil is needed to fry 6 potatoes, and he wants to fry 18 potatoes, then he'll end up using 3 gallons
