using System;
using System.Collections.Generic;
// NOT using System.Linq;

public class Example1{
  
  public static void Main(){

    // The average age of all females - basic version

    IEnumerable<int> ageSum = Person.SomePersons
       .MyWhere(p => p.Sex == Sex.Female)
       .MySelect(p => p.Age);

    double result =
       (double)(ageSum.MyAggregate((sum,i) => sum + i)) / 
       ageSum.MyCount();

   Console.WriteLine("Result = {0}", result);  // Result = 37,3333333333333
  }
}