- 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
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 5 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Conditional Probability
What does the notation P(A|B) mean?
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.
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.