Conditional Probability
Overview
Sometimes one event changes the chance of another. If you draw a counter from a bag and keep it, the next draw is from a smaller bag, so the probabilities shift. Conditional probability is the mathematics of these knock-on effects: the probability of one event given that another has already happened.
In this Extended topic you will work with conditional probability using tables, Venn diagrams and tree diagrams. The classic setting is drawing objects without replacement, where each draw alters what remains. Once you see how the branch probabilities change after the first event, problems that look hard become a tidy multiplication along a path.
Objectives
- Calculate conditional probability using Venn diagrams, tree diagrams and tables.
Audio Lesson
Listen to this lesson in the app
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Flashcards
Quick recall practice on the facts this topic is tested on.
Practise these cards in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on Conditional Probability. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- A bag has 5 red and 3 blue counters. Two are drawn without replacement. What is P(both red)? A. 25/64 B. 20/56 C. 5/8 D. 4/7 Answer: B
- After drawing one red from a bag of 5 red and 3 blue (kept out), what is the probability the next is red? A. 5/8 B. 5/7 C. 4/7 D. 4/8 Answer: C
- Of 18 French students, 12 also study Spanish. A French student is chosen. What is P(studies Spanish)? A. 1/3 B. 2/5 C. 2/3 D. 12/30 Answer: C
- Which rule gives the probability of A and B in general? A. P(A) + P(B) B. P(A) x P(B given A) C. P(A) - P(B) D. P(A) / P(B) Answer: B
- A bag has 4 white and 2 black balls. Two are drawn without replacement. What is P(both white)? A. 4/9 B. 2/5 C. 1/3 D. 12/30 Answer: B
Work through these questions in the app
Work through these questions in the app
Recommended Books
Practice Mock Questions
Want to practice mock questions on Conditional Probability? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
