private static void Main(string[] args)
{
List<Person> l1 = new List<Person>();
l1.Add(new Person("Ann", "Ray", 20));
l1.Add(new Person("Cary", "I", 12));
l1.Add(new Person("Helen", "Carr", 19));
List<Person> l2 = new List<Person>();
l2.Add(new Person("John", "Doz", 20));
l2.Add(new Person("Ray", "Smith", 19));
l2.Add(new Person("Viki", "Ol", 18));
Group gr1 = new Group(GroupNames.BackEnd, l1);
Group gr2 = new Group(GroupNames.FrontEnd, l2);
List<Group> glist = new List<Group>();
glist.Add(gr1);
glist.Add(gr2);
var queryresult = from p in glist select p.Students.Average(s => s.Age);
foreach (int d in queryresult)
{
Console.WriteLine(d.ToString());
}
Console.ReadLine();
}