Marica, sorry you feel that way. As I acknowledge in the video it can be frustrating to use any online homework because your answer must be precise. Webwork allows us to provide FREE, INSTANT feedback for students. We'll continue to explore options and work on improving all aspects of the course. Check out the other resources and tutoring options available.

+Shivani Thapar: Both are standard deviation. Sx is the 'sample standard deviation'. Sigma x is the 'population standard deviation'. As their names imply, you use Sx when you are working with a sample and you'd use sigma x if you have the whole population. For a look at the formulas and how they are different, I refer my students to: www.mathsisfun.com/data/standard-deviation.html

+Aspartem This calculator give you the standard deviation, which is by definition, the square root of the variance. Simply use the technique shown to get the standard deviation and then square it. I agree finding standard deviation/variance by hand is tedious. I believe that math courses should have students do it once 'by hand' and then introduce a technology to do the work for them.