University of California, Berkeley: Philip Stark's SticiGui: "Chapter 4: Measures of Location and Spread”
Read this chapter, which will show you all the necessary formulas for computing descriptive statistics for analyzing data from a sample such as the mean, median, mode, variance, range, and standard deviation. There are several exercises and Java applets embedded in the text that are meant to further reinforce your learning. Do not skip these exercises! For instructions on how to navigate these exercises, see "Special Instructions on SticiGui Exercises and Java applets” in the course information section.