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0580/42 May/Jun 2021, Question 1: Calculating with Bounds

Cambridge IGCSE Mathematics 0580 · Paper 42 (Extended) · Calculator · 11 marks

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The question, in short

Solve paint cost, ratio and coverage problems: find a sale price, cost for 42.5 litres, white percentage, green litres, and minimum 2.5-litre tins for a wall.

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

Part (ai) · 2 marks

Find the sale price of a 2.5-litre tin costing $13.50 after a 14% reduction.

  1. 1Sale price = 13.50 × (1 − 14/100) = 13.50 × 0.86
  2. 2= $11.61

Answer11.61

Part (aii) · 2 marks

Find the cost of 42.5 litres of paint at the sale price.

  1. 1Tins = 42.5 ÷ 2.5 = 17
  2. 2Cost = 17 × 11.61 = $197.37

Answer197.37

Part (bi) · 1 mark

Find the percentage of paint that is white in the ratio 2 : 8 : 5.

  1. 1White = 8/(2 + 8 + 5) × 100 = 8/15 × 100 = 53.33… ≈ 53.3%

Answer53.3 or 53.33…

Part (bii) · 2 marks

Find the litres of green paint in 22.5 litres using the ratio 2 : 8 : 5.

  1. 11 part = 22.5 ÷ 15 = 1.5
  2. 2Green = 5 × 1.5 = 7.5 litres

Answer7.5

Part (c) · 4 marks

Wall 20.5 m by 2.4 m, each to 1 d.p.; 1 litre covers 10 m². Find minimum 2.5-litre tins needed, showing working.

  1. 1Upper bounds: 20.5 + 0.05 = 20.55 m, 2.4 + 0.05 = 2.45 m
  2. 2Largest area = 20.55 × 2.45 = 50.3475 m²
  3. 3Paint = 50.3475 ÷ 10 = 5.03475 litres; tins = 5.03475 ÷ 2.5 = 2.01…
  4. 4She needs 3 tins

Answer3

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Also searched as: 0580/42/M/J/21 · 0580_s21_qp_42 · 0580 s21 42 · question 1.
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