The language of chance. Read two-way tables, apply the rules of probability, and reason about conditional probability and independence. Then meet random variables and the two workhorse models of the course — the binomial and the normal distribution — plus the sampling distributions that lead to inference.
Six ways to master Unit 2 — pick whichever fits how you like to study.
All 12 topics from the College Board CED, in order.
Unit 2 gives you the tools to reason about chance. It opens with two categorical variables — two-way tables and the marginal, joint, and conditional relative frequencies you read from them — then builds the rules of probability: the Law of Large Numbers, the addition rule for mutually exclusive events, conditional probability, and the multiplication rule for independent events. Simulation is used throughout to estimate probabilities when exact calculation is hard.
The unit then introduces random variables — rules that assign numbers to the outcomes of a chance process — and their probability distributions, each with a mean (expected value) and a standard deviation. You'll study the two most important models in the course: the binomial distribution (a fixed number of independent success/failure trials) and the normal distribution (the bell curve, with z-scores and the empirical rule). It closes with sampling distributions and the Central Limit Theorem, the bridge from probability to the inference of Units 3–5.
This unit is 15–25% of the AP Statistics exam and takes about 24 class periods. The four statistical practices below run through every topic: