University of California, Berkeley: Philip Stark's SticiGui: "Chapter 12: Counting"
Read Chapter 12 to study several of the most common formulas in probability. 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 onSticiGui Exercises and Java Applets” in the "Course Information” section above.