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4MA1/2HR Jun 2019, Question 20: Calculating with Bounds

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2HR (Higher) · Calculator · 3 marks

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The question, in short

Using x = 6a/(b − a) with a = 3.46 to 3 s.f. and b = 6.3 to 1 d.p., find the upper bound of x as a decimal to 3 s.f., showing working.

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Solution · 3 marks

  1. 1a = 3.46 correct to 3 significant figures, so upper bound of a is 3.465
  2. 2b = 6.3 correct to 1 decimal place, so lower bound of b is 6.25
  3. 3x = (6a) / (b − a)
  4. 4Substitute upper bound of a and lower bound of b: x = (6 × 3.465) / (6.25 − 3.465)
  5. 56 × 3.465 = 20.79
  6. 66.25 − 3.465 = 2.785
  7. 720.79 / 2.785 = 7.46499...
  8. 8Rounded to 3 significant figures: 7.46

Answer7.46

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