using System.Collections.Generic;
public int StudentID { get; set; }
public string StudentName { get; set; }
public string referenceId { get; set; }
public decimal charges { get; set; }
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);