4.5 & 4.6 Probability

What are the chances?

This unit is all about probability - the study of chance. For many students, much of this is revision of previous experiences with some new ideas thrown in. The unit covers the fundamental ideas, language notation, combined events and conditional probability. You will be expected to work with sample space, tree and Venn diagrams as well as reading from tables. This page has everything you need to learn, understand and practice working with these ideas.

Key Concepts

In this unit you should learn to…

  • recognise key terms

  • calculate using sample space diagrams

  • use tree diagrams

  • find probabilities from tables and Venn diagrams

  • use conditional probability

Essentials

Slides Gallery - Probability Part 1

This first section covers the ideas, language, notation as well as combined events with sample space and tree diagrams. Use these slides to review the material and key points covered in the videos.

1. Ideas, language and notation - Part 1

This is an introduction to the key ideas and terms in this study of probability.

2. Ideas, language and notation - Part 2

In this video we move on to more details about the idea, language and terminology.

3. Sample Space and Combined events

Sample space diagrams are a relatively straightforward way of looking outcomes for two combined events. Here we will look at one in the context of an example and how it can be used to deduce probabilities. We will cover the AND and OR rules for combined events here.

4. Tree Diagrams and Combined events

Here will look at how tree diagrams can achieve the same thing and go on to be more versatile than the sample space. We will cover the AND and OR rules for combined events here.

5. Tree Diagrams 'Without Replacement'

The idea of 'Without replacement' is a really important one. This is when the probabilities of a second event depend on the outcome of the previous event.

Slides - Probability part 2

This section covers the following - Probability from tables and Venn diagrams, Conditional probability and the laws of Probability. Use these slides to review the material and key points covered in the videos.

6. Probabilities from Tables

Often we can deduce probabilities from a simple table of results. Here we will look at such an example which will lead nicely into the later section on Conditional Probability.

7. Probabilities from Venn Diagrams

This section focusses on linking set theory, Venn diagrams and probability together. How we deduce probabilities from Venn diagrams?

8. Conditional Probability

This is a key concept to get your heads around. This section has three videos that go through conditional probability in the context of a) A table of results, b) A tree diagram and c) a Venn diagram. This idea is probably most easily understood from the 'Table of results' context and can be quite intuitive.

9. The Laws of Probability

These are sophisticated concepts that summarise in general, much of what is already understood by this point. Have at go at following and understanding the laws for Combined events, mutually exclusive events, independent events and conditional probability.

Summary

This section of the page can be used for quick review. The flashcards help you go over key points and the quiz lets you practice answering questions on this subtopic.

Revision Cards

Review these condensed 'key point' revision cards to help you check and keep ideas fresh in your mind.

Test Yourself

Self Checking Quiz

Practice your understanding on these quiz questions. Check your answers when you are done and read the hints where you got stuck. If you find there are still some gaps in your understanding then go back to the videos and slides above.

Exam Style Questions

The following questions are based on IB exam style questions from past exams. You should print these off (from the document at the top) and try to do these questions under exam conditions. Then you can check your work with the video solution.

Question 1

Video solution

Question 2

Video solution

Question 3

Video solution

Question 4

Video solution

Question 5

Video solution

Question 6

Ross and Dylan are playing padel. The probability that Dylan wins the first game is 0.6. If Ross wins the game the probability that he wins the next game is 0.9. If Dylan wins the game, the probability that he wins the next game is 0.5. Let R be the probability that Ross wins a game, and D be the probability that Dylan wins the game. 

a. Complete the tree diagram to represent the padel game. 

b. Find the probability that Dylan wins both games

c. Find the probability that Ross wins the second game, given that he wins the first game.

Video Solution

 

 

MY PROGRESS

How much of 4.5 & 4.6 Probability have you understood?