public static void Main() { Tomcat tomcat1 = new Tomcat("Tomcat", 13); Tomcat tomcat2 = new Tomcat("Tomcat", 3); Tomcat tomcat3 = new Tomcat("Tomcat", 10); Kitten kitten1 = new Kitten("Kitten", 1); Kitten kitten2 = new Kitten("Kitten", 1); Kitten kitten3 = new Kitten("Kitten", 9); Dog dog1 = new Dog("Dog", 15, Gender.Female); Dog dog2 = new Dog("Dog", 3, Gender.Male); Dog dog3 = new Dog("Dog", 7, Gender.Female); Frog frog1 = new Frog("Frog", 4, Gender.Female); Frog frog2 = new Frog("Frog", 0, Gender.Male); Frog frog3 = new Frog("Frog", 2, Gender.Female); IList<Animal> animals = new List<Animal> { tomcat1, tomcat2, tomcat3, kitten1, kitten2, kitten3, dog1, dog2, dog3, frog1, frog2, frog3 }; tomcat1.ProduceSound(); kitten1.ProduceSound(); dog1.ProduceSound(); frog1.ProduceSound(); double catsAverage = animals .Where(c => c is Cat) .Average(c => c.Age); double dogsAverage = animals .Where(c => c is Dog) .Average(c => c.Age); double frogsAverage = animals .Where(c => c is Frog) .Average(c => c.Age); Console.WriteLine("Average cats age: {0:F2}", catsAverage); Console.WriteLine("Average dogs age: {0:F2}", dogsAverage); Console.WriteLine("Average frogs age: {0:F2}", frogsAverage); }