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0580/13 Oct/Nov 2025, Question 26: Tree Diagrams for Independent Events

Cambridge IGCSE Mathematics 0580 · Paper 13 (Core) · Non-calculator · 4 marks

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The question, in short

Li faces two traffic light sets with stop probabilities 0.4 and 0.7; fill in the missing tree diagram values and find the chance he stops at neither set.

Summarised in our own words. Use the official paper for the exact wording and the diagram.

Part (a) · 2 marks

Fill in the missing probability values on the tree diagram branches.

  1. 1First set: Does not stop = 1 − 0.4 = 0.6
  2. 2Second set, after each first branch: Stops 0.7, Does not stop 1 − 0.7 = 0.3

AnswerCorrect tree diagram

Part (b) · 2 marks

Calculate the probability that Li stops at neither of the two traffic light sets.

  1. 1P(not stop, not stop) = 0.6 × 0.3
  2. 2= 0.18

Answer0.18

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