Week 5 — Probability Foundations

Welcome to your Week 5 Start Here page.

Why this matters

Chance runs through daily work. A pharmacist weighing the risk of a side effect and a travel planner judging a connecting flight both reason with the same few probability rules you learn this week.

In plain language

Chance is part of almost every decision you make, from carrying an umbrella to trusting a test result. This week you learn to put a number on chance, called a probability (a number from 0 to 1 that says how often something happens in the long run). You will list every way a situation can turn out and count the ways you care about. You will learn three short rules for "not", "or", and "and". Then you will see how one piece of news, such as which island a penguin lives on, can change a chance, which is the idea of a conditional probability (a chance worked out after you learn something new).

• Already covered: Weeks 1 to 4 described data you already have, ending with two variables at once.
• This week: probability: long-run frequency, sample spaces, three rules, conditional probability, and independence.
• How they connect: Week 4's conditional distribution becomes a conditional probability.
• Where we're going next: a new unit on chance; Week 6, Random Variables, attaches numbers to outcomes.

Focus

How likely is that, and does one piece of news change the chance? This week you count outcomes and use four short rules.

By the end of this module, you should be able to:

• [ ] read a probability as a long-run share and reject a "due" streak
• [ ] list a sample space and use the complement, addition, and multiplication rules
• [ ] read a conditional probability off a two-way table in the right direction
• [ ] check two events for independence

To-do

Plan your week

1. Read Chapter 5 (about 40 minutes), then the lecture and slides.
2. Work the lecture tutorial (60–90 minutes) and the practice set (about 20 minutes).
3. Do the Data Lab (about 90 minutes), the discussion, and the assignment.
4. Take the quiz.

This week's checkpoint: find P(Gentoo | Biscoe) from the penguin table and say why it differs from P(Biscoe | Gentoo).

You've got this

Take it in order, and ask your instructor early if a step snags.

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