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0580/33 Oct/Nov 2022, Question 9: Basic Probability

Cambridge IGCSE Mathematics 0580 · Paper 33 (Core) · Calculator · 7 marks

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The question, in short

Use bag probabilities with 35 counters to find yellow count, then complete a two-pick tree diagram for 15 counters and find the probability of two browns.

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

Part (a) · 3 marks

Given 6 pink, 8 blue, green probability 2/7 out of 35 counters, find how many are yellow.

  1. 1Green = 2/7 × 35 = 10
  2. 2Yellow = 35 − 6 − 8 − 10 = 11

Answer11

Part (bi) · 2 marks

Fill in the missing branch probabilities on the tree diagram for two draws with replacement from 7 red and 8 brown.

  1. 1First counter: Brown = 1 − 7/15 = 8/15
  2. 2Replaced, so second pick is the same each time: Red 7/15, Brown 8/15 on both branches

AnswerFirst counter: Brown 8/15 Second counter after Red: Red 7/15, Brown 8/15 Second counter after Brown: Red 7/15, Brown 8/15

Part (bii) · 2 marks

Calculate the probability that both counters Mateo picks are brown.

  1. 1P(brown, brown) = 8/15 × 8/15 = 64/225

Answer64/225

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