ProbabilityKey Facts

Key Facts

Part of Conditional Probability — GCSE Mathematics

This key facts covers Key Facts within Conditional Probability for GCSE Mathematics. Revise Conditional Probability in Probability for GCSE Mathematics with 14 exam-style questions and 12 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 2 of 4 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.

Topic position

Section 2 of 4

Practice

14 questions

Recall

12 flashcards

Key Facts

Conditional Probability: P(A|B) = probability of A given B has occurred
Formula: P(A|B) = P(A ∩ B) / P(B)
Read P(A|B) as "probability of A given B"
The given condition becomes the new sample space
P(B) must be greater than 0 for the formula to work
Used in tree diagrams for dependent events

Practice Questions for Conditional Probability

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.

3 markshigher

Quick Recall Flashcards

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.

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.

Key Facts

Key Facts

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Practice Questions for Conditional Probability

Quick Recall Flashcards

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