public static void Main(string[] args)
    {

      int[][] arr = new int[5][];
      arr[0] = new int[8];
      arr[1] = new int[8];
      arr[2] = new int[8];
      arr[3] = new int[8];
      arr[4] = new int[8];

      Random rdm = new Random();

      for (int i = 0; i < arr.Length; i++)
      {
        for (int j = 0; j < 8; j++)
        {
          arr[i][j] = rdm.Next(31);
        }
      }

      foreach (int[]a in arr)
      {
        foreach (int b in a)
        {
          Console.Write("{0},", b);
        }
        Console.WriteLine("");
      }
   
    }