using System;

using System.Collections.Generic;

using System.Linq;

    public class Student

    {

        public int StudentID { get; set; }

        public string StudentName { get; set; }

        public string referenceId { get; set; }

        public decimal charges { get; set; }

    }

​

public class Program

{

    public static void Main()

    {

          IList<Student> studentList = new List<Student>() {

                new Student(){ StudentID=1, StudentName="Bill",referenceId = "43", charges = 340},

                new Student(){ StudentID=2, StudentName="Steve",referenceId = "43", charges = 340},

                new Student(){ StudentID=3, StudentName="Ram",referenceId = "43", charges = 340},

                new Student(){ StudentID=1, StudentName="Moin",referenceId = "41", charges = 281}

            };

​

​

            var sum = studentList.GroupBy(x => x.referenceId).Select(x=>x.FirstOrDefault()).Sum(s => s.charges);

            Console.WriteLine("Sum {0}",sum);

​

    }

​

}