The most important topics in this course are covered in the Section 4.3 - 4.5 videos and WebAssignments. Everything you learn in these sections counts double. Why do I say that? It's because these are not only the most substantive and useful topics in Part 4, but they're also absolutely essential for the probability applications that appear in Part 5. Most of the time when a student complains "I don't understand probability," what it really indicates is that the student doesn't understand the counting techniques introduced in Part 4 that are so useful in probability models. So believe me, the depth of your understanding of the last 3 sections of Part 4 will heavily affect your grade not only on Test #2 but also on Test #3.