It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
DIY Maths: Range, variation and standard deviation
Mathsisfun.com does a good job of explaining how to find variance and standard deviation. At the end of this page, you will find a quiz to test your knowledge. For a more advanced discussion, see www.onlinemathlearning.com/variance.html.