PHP arrays homework

using System;

namespace misc
{
    internal class Program
    {
        static void Main(string[] args)
        {
            // average(arithmetic mean, средно аритметично)
            int[] arr = { 3,4,5,6,7,8,9};
            int sum = 0;
            for (int i = 0; i < arr.Length; i++)
            {
                sum += arr[i];
            }

            int average = sum / arr.Length;
            string arrToString = string.Join(' ', arr);
            Console.WriteLine($"average of [{arrToString}] is: {average:0.00}"); //:0.00 forces the output to be printed with 2 decimals.

            // geometric mean (средно геометрично)


            int product = 1;
            for (int i = 0; i < arr.Length; i++)
            {
                product *= arr[i];
            }

            double geometricMean = Math.Pow((double)product, (1/(double)arr.Length)); //(double) is for casting to double since Math.Pow works with floats and doubles and not ints.
            // 1/power == nth-root
            Console.WriteLine($"geometric mean of [{arrToString}] is: {geometricMean:0.00}");

            //root mean square - средноквадратично (wiki) - домашното по PHP
            int sumOfSquares = 0;
            for (int i = 0; i < arr.Length; i++)
            {
                sumOfSquares += arr[i] * arr[i];
            }

            //homework assignment states sqrt(sum num^2)
            double rootMeanSquare = Math.Sqrt(sumOfSquares) / arr.Length; // since math.sqrt returns a double, , '/' is considered a floating point division and not integer division (5.0/2=2.5)
            Console.WriteLine($"geometric mean of [{arrToString}] is: {rootMeanSquare:0.00}");

        }
    }
}