C#

private static int FactorialRecursive(int x)
    {
    return (x > 1 ? x * FactorialRecursive(x - 1) : 1);
    }
private static int FactorialIterative(int x)
    {
    int f = 1;
    while (x > 1)
        {
        f *= x--;
        }
    return f;
    }

private int CalculateProbabilityOfDrawNumbersFromAllNumbers(int drawNumbers, int allNumbers)
{
    return ((Factorial(allNumbers) * Factorial(80 - allNumbers)) / (((Factorial(80) * ((Factorial(drawNumbers) * Factorial(allNumbers - drawNumbers)) * (Factorial(20 - drawNumbers) * Factorial(((80 - allNumbers) - (20 - drawNumbers)))))) / (Factorial(20) * Factorial(80 - 20)))));
}

private static int Factorial(int x)
{
    int f = 1;
    while (x > 1)
    {
        f *= x--;
    }
    return f;
}

using System.IO;
using System;

class Program
{
    static void Main()
    {
        Console.WriteLine(CalculateProbabilityOfDrawNumbersFromAllNumbers(1,1));
    }
    private static double CalculateProbabilityOfDrawNumbersFromAllNumbers(double drawNumbers, double allNumbers)
        {
            return Factorial(allNumbers) / (Factorial(drawNumbers) * Factorial(allNumbers - drawNumbers)) * (Factorial(80 - allNumbers) / (Factorial(20 - drawNumbers) * Factorial(80 - allNumbers - (20 - drawNumbers)))) / (Factorial(80) / (Factorial(20) * Factorial(80 - 20)));
        }

        private static double Factorial(double x)
        {
            double f = 1;
            while (x > 1)
            {
                f *= x--;
            }
            return f;
        }
}

Console.WriteLine((CalculateProbabilityOfDrawNumbersFromAllNumbers(12,12) * 100).ToString("F7").TrimEnd(new Char[] { '0' } ).TrimEnd(new Char[] { '.' } )+"%");

Quote:

im not sure why i was getting division by zero error. the int has surpass its largest number and return 0?

Exoskeletor wrote:

Wow it really works as the counters we have in cars that counts kilometers?

Bastard Programmer from Hell
"If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.