using System;

public class Program

{

    public static void Main()

    {

        double? amount = 1000;

        bool isPartial = true;

        double percent = 50;

        var result = amount ?? 0 * (isPartial == true ? percent : 100)/100;

        Console.WriteLine("Wrong Result");

        Console.WriteLine(result);

        //Correct way 

        result = (amount ?? 0) * (isPartial == true ? percent : 100)/100;

        Console.WriteLine("Correct Result");

        Console.WriteLine(result);

    }

}