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4MA1/2H Nov 2021, Question 9: Standard Form

Pearson Edexcel International GCSE Mathematics A 4MA1 · Paper 2H (Higher) · Calculator · 5 marks

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The question, in short

Calculate bacteria per raindrop from 1.75 × 10⁶ bacteria and 2.4 × 10⁷ raindrops, then find molecules in the tank using 5.01 × 10²¹ atoms per drop with atoms three times molecules.

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Part (a) · 3 marks

Divide 1.75 × 10⁶ by 2.4 × 10⁷ and give the bacteria per raindrop in standard form to 2 significant figures.

  1. 1Bacteria per raindrop = 1.75 × 10⁶ ÷ 2.4 × 10⁷
  2. 2= 0.072916…
  3. 3= 7.2916… × 10⁻²
  4. 4= 7.3 × 10⁻² (2 s.f.)

Answer7.3 × 10⁻²

Part (b) · 2 marks

Use 5.01 × 10²¹ atoms per drop and the 3:1 atom-to-molecule ratio to find total molecules in the tank, standard form to 1 significant figure.

  1. 1Atoms in the tank: 2.4 × 10⁷ × 5.01 × 10²¹ = 1.2024 × 10²⁹
  2. 2Molecules = atoms ÷ 3 = 4.008 × 10²⁸
  3. 3= 4 × 10²⁸ (1 s.f.)

Answer4 × 10²⁸

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