using System;

​

var Data = new[] { 1.0, 5.0, 25.0 };

double sumOfSquares = 0.0;

double total = 0.0;

foreach (double d in Data)

{

        total += d;

        sumOfSquares += Math.Pow(d, 2);

}

​

int count = Data.Length;

double variance = ((count * sumOfSquares) - Math.Pow(total, 2)) / (count * (count - 1));

​

Console.WriteLine( Math.Round(variance, 4))