Let's review!
In this unit you learned to count without listing. You started with the multiplicative and additive counting principles and indirect counting. You used factorials and permutations P(n, r) for ordered arrangements, handled conditions with blocks, gaps and cases, and counted arrangements with repetition and identical objects. You met combinations C(n, r) for selections where order does not matter, and connected them to Pascal's triangle, routes on a grid and the binomial theorem. Finally, you used all of these to find probabilities of equally likely outcomes.
The next unit, Discrete Probability Distributions, builds directly on this one: the binomial and hypergeometric distributions are made of the combinations you have practised here.
How to use this review
Work through one or two sections at a time. Before calculating, write one line saying which tool you will use and why ("order matters, no repeats: P(n, r)"). That decision is where most errors happen. Check answers with a second method when you can (list a small case, use the complement, or solve it two ways). For each question you miss, note why: added instead of multiplied? used P instead of C? missed a case? Then revisit the lesson named in the section title. Finish with the 10-question quiz.