4MA1/2H Jan 2019, Question 3: Basic Probability
Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2H (Higher) · Calculator · 4 marks
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The question, in short
Bag has 90 counters, red to blue ratio 2:13. Extra red counters are added until the chance of picking red at random is 1/3. Find how many red counters are added.
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Solution · 4 marks
- 1One share: 90 ÷ (2 + 13) = 6
- 2Red = 2 × 6 = 12, blue = 13 × 6 = 78
- 3Add x red counters: (12 + x)/(90 + x) = 1/3
- 43(12 + x) = 90 + x, so 36 + 3x = 90 + x
- 52x = 54, so x = 27
Answer27
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