//14

int years1 = 10;
int count1 = 0;
int count2 = 0;
        
for (int year = 1; year <= years1; year++)
{
    for (int month = 1; month <= 12; month++)
    {
        DateTime date1 = new DateTime(year, month, 13);
        if (date1.DayOfWeek == DayOfWeek.Friday)
        {
            count1++;
        }
        count2++;
    }
}

Console.WriteLine("Вероятности выпадения 13 числа каждого месяца на:");
Console.WriteLine("Понедельник: " + (double)CountOfThirteenths(DayOfWeek.Monday) / count2);
Console.WriteLine("Вторник: " + (double)CountOfThirteenths(DayOfWeek.Tuesday) / count2);
Console.WriteLine("Среда: " + (double)CountOfThirteenths(DayOfWeek.Wednesday) / count2);
Console.WriteLine("Четверг: " + (double)CountOfThirteenths(DayOfWeek.Thursday) / count2);
Console.WriteLine("Пятницу: " + (double)count1 / count2);
Console.WriteLine("Субботу: " + (double)CountOfThirteenths(DayOfWeek.Saturday) / count2);
Console.WriteLine("Воскресенье: " + (double)CountOfThirteenths(DayOfWeek.Sunday) / count2);

static int CountOfThirteenths(DayOfWeek day)
{
    int count3 = 0;
    for (int year = 1; year <= 10; year++)
    {
        for (int month = 1; month <= 12; month++)
        {
            DateTime date1 = new DateTime(year, month, 13);
            if (date1.DayOfWeek == day)
            {
                count3++;
            }
        }
    }
    return count3;
}