Probability — A-Level Mathematics Revision

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What is Probability?

Probability at A-Level builds on GCSE concepts by introducing conditional probability, Venn diagrams, and tree diagrams for more complex scenarios. You will learn to use probability formulae and understand the concepts of independence and mutual exclusivity.

Board notes: All A-Level Maths boards (AQA, Edexcel, OCR) cover probability in a similar way. The complexity of the problems and the use of Venn diagrams and tree diagrams are consistent across all boards.

Worked example

Common mistakes

• 1Confusing the concepts of independence and mutual exclusivity. Two events are independent if the occurrence of one does not affect the probability of the other, while two events are mutually exclusive if they cannot both happen at the same time.
• 2Incorrectly using the formula for conditional probability, P(A|B) = P(A and B) / P(B).
• 3Making errors in setting up or interpreting Venn diagrams, particularly with the placement of probabilities in the correct regions.

Probability exam questions

Exam-style questions for Probability with mark-scheme style solutions and timing practice. Aligned to AQA, Edexcel and OCR specifications.

Frequently asked questions

• What is the difference between P(A and B) and P(A or B)?

  P(A and B) is the probability that both event A and event B occur. P(A or B) is the probability that either event A or event B or both occur. The formula is P(A or B) = P(A) + P(B) - P(A and B).

• How do I know if two events are independent?

  Two events A and B are independent if P(A and B) = P(A) * P(B). If this condition is not met, the events are not independent.