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4MA1/2H Jan 2020, Question 14: Tree Diagrams for Dependent Events

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2H (Higher) · Calculator · 4 marks

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The question, in short

Cupboard holds 20 glasses: 13 large, 7 small. Roberto picks two at random. Complete the tree diagram and find the probability both are small.

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

Part (a) · 2 marks

Fill in the missing probabilities on the two-stage tree diagram for picking two glasses without replacement.

  1. 1First branch: 13/20 for large, 7/20 for small
  2. 2Second branch after large: 12/19 for large, 7/19 for small
  3. 3Second branch after small: 13/19 for large, 6/19 for small

AnswerFirst branches: large 13/20, small 7/20; after large: large 12/19, small 7/19; after small: large 13/19, small 6/19

Part (b) · 2 marks

Calculate the probability that both glasses Roberto takes are small.

  1. 17/20 × 6/19
  2. 242/380
  3. 321/190

Answer21/190

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