Try this :
using System;
class StdDeviation
{
public static void Main()
{
float [] nos = {3.5F,57,2,6,24,14,95,23,74,23};
int n = nos.Length;
float sum = 0.0F,sumofsq = 0.0F, mean;
double deviation;
Console.Write("Array List consists of : ");
for (int i = 0; i < n; i ++)
{
Console.Write(nos[i] + " ");
}
for (int i = 0; i < n; i ++)
{
sum = sum + nos[i];
}
for (int i = 0; i < n; i ++)
{
sumofsq = sumofsq + (nos[i]*nos[i]);
}
mean = sum / n;
deviation = Math.Sqrt(sumofsq / 8.0);
Console.WriteLine("\n\n Sum = " +sum);
Console.WriteLine("\n Mean = " +mean);
Console.WriteLine("\n Deviation = " +deviation );
Console.ReadLine();
}
}