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4MA1/1FR Jan 2019, Question 10: Basic Probability

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

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The question, in short

From a box of 20 beads (7 red, 11 green, rest yellow), find probabilities of drawing colours; then from 26 counters (5 pink, 10 blue, rest white) after adding pink and removing blue, find the blue probability given pink is 1/2.

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

Part (a) · 1 mark

State the probability that a bead drawn at random from the box is red.

  1. 17 red beads out of 20 total beads
  2. 27 / 20 = 7/20

Answer7/20

Part (b) · 2 marks

Find the probability that a randomly drawn bead is either red or yellow.

  1. 120 − 7 - 11 = 2 yellow beads
  2. 22 + 7 = 9 red or yellow beads
  3. 39 / 20 = 9/20

Answer9/20

Part (c) · 3 marks

After the changes keep 26 counters and pink probability is 1/2, find the probability of drawing a blue counter.

  1. 11/2 of 26 = 13 pink counters in the end
  2. 2Started with 5 pink, so added 8 pink
  3. 3To keep total at 26, must have removed 8 blue
  4. 4Started with 10 blue, removed 8, so 2 blue left
  5. 52 / 26 = 2/26

Answer2/26

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