gistfile1.txt

using System;
 
public class Math
{
    public virtual int Sum(int a , int b)
    {
        return a+b;
    }
}

public class Class1 : Math
{
    public  int Sum(int a, int b)
    {
        return a + b + 10;
    }
}

public class Class2 : Math
{
    public override int Sum(int a, int b)
    {
        return a + b + 10;
    }
}

class Program
{
    static void Main()
    {
        Math math1 = new Class1();
        Math math2 = new Class2();
        
        Console.WriteLine(math1.Sum(5, 3)); // Prints 8
        Console.WriteLine(math2.Sum(5, 3)); // Prints 18
    }
}

thanks Jon Skeet I get your Idea that If we write the same method as base class the compiler ignore the derived class . thanks a lot and I delete my question