A-level · Probability

Tree diagrams and sequential eventsExam-style questions

Using a tree diagram for two-stage experiments: multiply probabilities ALONG the branches of a path (AND), add across the paths that make up an event (OR), and use 1 − P(none) for "at least one". The crucial distinction between sampling WITH replacement (probabilities stay the same) and WITHOUT replacement (the totals, and so the later probabilities, change).

Start practising Read the lesson

12 questions · A-level level · mark scheme and worked solution on each · no sign-up to try

DifficultyAllLevel 2Level 3Level 4Level 5
  1. 1
    A bag contains 55 red and 33 blue counters. Two are drawn at random, with replacement. Find the probability that both are red.
    Level 2 · 2 marksTry it