4.  public static boolean isSorted(double[] data)
    {
        for (int i=1; i<data.length; i++)
        {
            if (data[i] < data[i-1])
            {
                return false;
            }
        }
        return  true;
    }

6.     public static void main(String[] args)
    {
        int[] a = {1,-2,4,-4,9,-6,16,-8,25,-10};
        double sumA = 0;
        int count = 0;
        for (int i = 0;i<a.length;i++)
        {
            sumA = sumA + a[i];
            count++;
        }
        double avg = (sumA/count);
        System.out.println("avg = "+ avg);

        double numerator = 0;
        for(int j = 0;j<a.length;j++)
        {
            numerator += Math.pow(a[j]-avg,2);
            System.out.println("num" + j + "= " + numerator);
        }
        double inRoot = numerator/(a.length-1);
        double end = Math.sqrt(inRoot);
        System.out.println(end);
    }