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0580/43 May/Jun 2021, Question 1: Compound Interest

Cambridge IGCSE Mathematics 0580 · Paper 43 (Extended) · Calculator · 14 marks

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The question, in short

Work through ratio sharing, percentage sale prices, compound salary growth, and combined percentage population change problems, finding totals, prices, years and overall percentage.

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

Part (ai) · 2 marks

Yasmin and Zak share money in ratio 21:19, Yasmin gets $6 more; find the total shared.

  1. 1Difference in ratio = 21 − 19 = 2 parts
  2. 22 parts = $6, so 1 part = 6 ÷ 2 = $3
  3. 3Total = (21 + 19) × 3 = 40 × 3 = $120

Answer120

Part (aiia) · 2 marks

A blouse originally $40 is reduced by 15% in a sale; find its sale price.

  1. 1Reduction = 15/100 × 40 = $6
  2. 2Sale price = 40 − 6 = $34

Answer34

Part (aiib) · 2 marks

A shirt's sale price is $29.75 after a 15% reduction; find its original price.

  1. 1Sale price = 85% of original: 0.85 × p = 29.75
  2. 2p = 29.75 ÷ 0.85 = $35

Answer35

Part (bi) · 3 marks

Xavier's salary $40 100 in 2010 rises 2% yearly; find his 2015 salary to the nearest dollar.

  1. 1Salary in 2015 = 40 100 × 1.02⁵
  2. 2= 44 273.64…
  3. 3≈ $44 274

Answer44 274

Part (bii) · 3 marks

With salary $40 100 in 2010 rising 2% yearly, find the first year it exceeds $47 500.

  1. 12018 (8 years): 40 100 × 1.02⁸ = 46 983.54…, less than 47 500
  2. 22019 (9 years): 40 100 × 1.02⁹ = 47 923.21…, greater than 47 500
  3. 3First year greater than $47 500: 2019

Answer2019

Part (c) · 2 marks

Town population rose 5% from Jan 2018 to Jan 2020, then fell 2% to Jan 2021; find overall percentage increase.

  1. 1Multiplier = 1.05 × 0.98 = 1.029
  2. 2Overall increase = (1.029 − 1) × 100 = 2.9%

Answer2.9

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Also searched as: 0580/43/M/J/21 · 0580_s21_qp_43 · 0580 s21 43 · question 1.
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