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4MA1/1HR Jun 2019, Question 14: Tree Diagrams for Dependent Events

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 1HR (Higher) · Calculator · 6 marks

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The question, in short

Given daily bus probability 0.3, lateness 0.2 by bus and 0.1 walking, complete a probability tree and estimate late days out of 200.

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

Part (a) · 2 marks

Fill in the missing branch probabilities on the tree, including walk and the late/not late branches from both bus and walk.

  1. 1The probability of walking is 1 − 0.3 = 0.7
  2. 2The probability of being late given he takes the bus is 0.2
  3. 3The probability of not being late given he takes the bus is 1 − 0.2 = 0.8
  4. 4The probability of being late given he walks is 0.1
  5. 5The probability of not being late given he walks is 1 − 0.1 = 0.9

Answer0.7, 0.2, 0.8, 0.1, 0.9

Part (b) · 4 marks

Using the tree, estimate how many of Barney's 200 college days next year he will be late.

  1. 10.3 × 0.2 = 0.06
  2. 20.7 × 0.1 = 0.07
  3. 30.06 + 0.07 = 0.13
  4. 40.13 × 200 = 26

Answer26

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