EDEXCEL GCSE MATHS · FOUNDATION & HIGHER
Exam Practice: Growth and Decay
Growth and decay · Multiplicative reasoning · Lesson 1 of 4 · 19 marks · 30 minutes
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Instructions
• Answer all the questions.
• Write your answers in the spaces provided.
• The marks for each question are shown in brackets - use this as a guide to how much to write.
• The answers are on separate pages at the back. Attempt every question before you look at them.
• Answer all questions. Show your working.
Question 1 CALCULATOR (3 marks)
£5000 is invested at 3% compound interest per year. Work out the value of the investment after 4 years. Give your answer to the nearest penny.
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(Total for Question 1 = 3 marks)
Question 2 CALCULATOR (3 marks)
A car is worth £12 000. Its value falls by 15% each year. Work out its value after 3 years.
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(Total for Question 2 = 3 marks)
Question 3 CALCULATOR (3 marks)
A culture has 500 bacteria. The number increases by 20% every hour. Work out the number of bacteria after 6 hours. Give your answer to the nearest whole number.
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(Total for Question 3 = 3 marks)
Question 4 CALCULATOR (4 marks)
The graph shows the number of bacteria in a culture, N, after t hours. The graph is a curve. (a) Use the graph to estimate the number of bacteria after 3.5 hours. (b) Use the graph to estimate the time when there are 200 bacteria.
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(Total for Question 4 = 4 marks)
Question 5 NON-CALCULATOR (3 marks)
A radioactive sample has a mass of 80 g. Its mass halves every 10 days. Work out its mass after 30 days.
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(Total for Question 5 = 3 marks)
Question 6 CALCULATOR (3 marks)
The population of a town is 2000. It decreases by 5% each year. Work out the population after 10 years. Give your answer to the nearest whole number.
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(Total for Question 6 = 3 marks)
TOTAL FOR PAPER = 19 MARKS
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Answers and mark scheme
Check your answer only once you have written one.
Question 1 (3 marks)
5000 × 1.03⁴ = 5627.54.
• Multiplier 1.03 M1
• 5000 × 1.03⁴ M1
• 5627.54 A1
Question 2 (3 marks)
12 000 × 0.85³ = 7369.50, so £7369.50.
• Multiplier 0.85 M1
• 12 000 × 0.85³ M1
• 7369.50 A1
Question 3 (3 marks)
500 × 1.2⁶ = 1492.99, so 1493.
• Multiplier 1.2 M1
• 500 × 1.2⁶ M1
• 1493 A1
Question 4 (4 marks)
(a) About 190 (accept 185 to 195). (b) About 3.8 hours (accept 3.7 to 3.9).
• (a) Reading at t = 3.5 M1
• (a) 190 (185 to 195) A1
• (b) Reading at N = 200 M1
• (b) 3.8 (3.7 to 3.9) A1
Question 5 (3 marks)
30 days is 3 halvings, so 80 × 0.5³ = 10 g.
• 3 halvings M1
• 80 × ⅛ M1
• 10 A1
Question 6 (3 marks)
2000 × 0.95¹⁰ = 1197.47, so 1197.
• Multiplier 0.95 M1
• 2000 × 0.95¹⁰ M1
• 1197 A1