New
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Lesson 8 of 16
New
New
- Year 8
Decrease by a percentage
I can calculate percentage changes (decrease).
Lesson details
Key learning points
- A bar model can be used to find a percentage decrease.
- A double number line can be used to find a percentage decrease.
- A ratio table can be used to find a percentage decrease.
- 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 (2025), 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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Prior knowledge starter quiz
6 Questions
Q1.40% of 120 is .
40% of 120 is .
Q2.22% of 520 is .
22% of 520 is .
Q3.31% of 440 is .
31% of 440 is .
Q4.Which of the following calculations is equivalent to 49% of 200?
Which of the following calculations is equivalent to 49% of 200?
49 × 200
100 − 20
Q5.Match each calculation with the equivalent percentage statement.
Match each calculation with the equivalent percentage statement.
Q6.19% of 840 is .
19% of 840 is .
Assessment exit quiz
6 Questions
Q1.Decrease 40 by 20%.
Decrease 40 by 20%.
Q2.Decrease 700 by 30%.
Decrease 700 by 30%.
Q3.Match each question to an equivalent question.
Match each question to an equivalent question.
Q4.Match each statement with the correct multiplier.
Match each statement with the correct multiplier.
Q5.Decrease 600 by 39%.
Decrease 600 by 39%.
Q6.Match each calculation to its answer.
Match each calculation to its answer.
