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Conditional Probability

Revise Conditional Probability in Probability for GCSE Mathematics with 14 exam-style questions and 12 flashcards. This is a high-frequency exam topic, so students should expect to explain it clearly under timed conditions.

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Probability That Depends on Context

Introduction 2

Key Facts

Key Facts 3

Calculating Conditional Probability

Deep Dive 4

Exam Tips

Sample Flashcards

What is conditional probability?

The probability of one event occurring given that another event has already occurred. It restricts the sample space to only the outcomes where the condition is met.

What does the vertical bar | mean in P(A|B)?

It means 'given that'. P(A|B) is read as 'the probability of A given B'. The event after the bar is the condition — it is already known to have occurred.

Sample Questions

What does the notation P(A|B) mean?

A. The probability of A and B both occurring
B. The probability of A occurring given that B has already occurred
C. The probability of A or B occurring
D. The probability of A occurring divided by the probability of B occurring

1 markfoundation

P(A) = 0.4, P(B) = 0.3 and P(A ∩ B) = 0.12. Using conditional probability, determine whether A and B are independent events. You must show all your working and give a reason for your conclusion.

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