using System;

public delegate void Calculation(int a, int b);             

public class Program

{

    static void addition(int a ,  int b)

    {

        Console.WriteLine(a+b);

    }

    static void mult(int a ,  int b)

    {

        Console.WriteLine(a*b);

    }

    static void division(int a ,  int b)

    {

        Console.WriteLine(a/b);

    }

    static void sub(int a ,  int b)

    {

        Console.WriteLine(a-b);

    }

    public static void Main()

    {

        Calculation c = new Calculation(addition);

        c += sub;

        c +=mult;

        c.Invoke(20,10);

​

    }

}