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0580/11 May/Jun 2025, Question 19: Tree Diagrams for Independent Events

Cambridge IGCSE Mathematics 0580 · Paper 11 (Core) · Non-calculator · 5 marks

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The question, in short

A box has 10 counters, red or green in ratio 1:4. Shareen picks twice with replacement. Complete the tree diagram and find the probability both counters are green.

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

Part (a) · 3 marks

Fill in the six missing probabilities on the tree diagram for the first and second picks.

  1. 1Red : green = 1 : 4, so red = 1/5, green = 4/5
  2. 2The counter is replaced, so the second picks are the same
  3. 3Write 1/5 on every Red branch and 4/5 on every Green branch

AnswerRed 1/5 and green 4/5 on every pair of branches

Part (b) · 2 marks

Calculate the probability that the two counters picked are both green.

  1. 1Red : green = 1 : 4, so P(green) = 4/5.
  2. 2The counter is put back, so P(green) stays 4/5.
  3. 3P(green, green) = 4/5 × 4/5 = 16/25

Answer16/25

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Also searched as: 0580/11/M/J/25 · 0580_s25_qp_11 · 0580 s25 11 · question 19.
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