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Year 8

Decrease by a percentage

I can calculate percentage changes (decrease).

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New
New
Year 8

Decrease by a percentage

I can calculate percentage changes (decrease).

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Share activities with pupils
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Lesson details

Key learning points

  1. A bar model can be used to find a percentage decrease.
  2. A double number line can be used to find a percentage decrease.
  3. A ratio table can be used to find a percentage decrease.
  4. In all of these representations a single multiplier can be used to find a percentage decrease.

Keywords

  • Proportionality - If two things are proportional then the ratio of part to whole is maintained and the multiplicative relationship between parts is also maintained.

Common misconception

Pupil can often get confused with increasing and decreasing an amount e.g Increase 45 by 23% and decreasing 45 by 23% have the same multiplier.

Encourage students to draw double number lines or ratio tables so they can see the increase and multiplier or decrease and multiplier.

To embed the understanding that many questions can be the same but written indifferent ways, get pupils to write as many different questions to a calculation on MWB e.g 0.65 x 500 = 65% of 500 = 500 decreased by 500 = 50% of 650 e.g 1.23 x 400 = increase 400 by 23% = find 123% of 400.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
40% of 120 is .
Correct Answer: 48
Q2.
22% of 520 is .
Correct Answer: 114.4
Q3.
31% of 440 is .
Correct Answer: 136.4, 136.40
Q4.
Which of the following calculations is equivalent to 49% of 200?
Correct answer: 0.49 × 200
49 × 200
Correct answer: 100 − 2
100 − 20
Q5.
Match each calculation with the equivalent percentage statement.
Correct Answer:0.12 × 560,12% of 560

12% of 560

Correct Answer:0.21 × 560,21% of 560

21% of 560

Correct Answer:0.012 × 560,1.2% of 560

1.2% of 560

Correct Answer:0.021 × 560,2.1% of 560

2.1% of 560

Q6.
19% of 840 is .
Correct Answer: 159.6, 159.60

Exit quiz

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6 Questions

Q1.
Decrease 40 by 20%.
Correct Answer: 32
Q2.
Decrease 700 by 30%.
Correct Answer: 490
Q3.
Match each question to an equivalent question.
Correct Answer:Decrease 450 by 12%,Work out 88% of 450

Work out 88% of 450

Correct Answer:Decrease 450 by 20%,Work out 80% of 450

Work out 80% of 450

Correct Answer:Decrease 450 by 80%,Work out 20% of 450

Work out 20% of 450

Correct Answer:Decrease 450 by 1.2%,Work out 98.8% of 450

Work out 98.8% of 450

Q4.
Match each statement with the correct multiplier.
Correct Answer:Decrease by 22%,×0.78

×0.78

Correct Answer:Decrease by 2%,×0.98

×0.98

Correct Answer:Decrease by 80%,×0.2

×0.2

Correct Answer:Decrease by 8%,×0.92

×0.92

Q5.
Decrease 600 by 39%.
Correct Answer: 366
Q6.
Match each calculation to its answer.
Correct Answer:Decrease 460 by 21%,363.4

363.4

Correct Answer:Decrease 800 by 52%,384

384

Correct Answer:Decrease 70 by 2%,68.6

68.6

Correct Answer:Decrease 400 by 12%,352

352