New
New
Year 10
Foundation

Checking and securing understanding of percentage decrease

I can decrease an amount by a given percentage.

New
New
Year 10
Foundation

Checking and securing understanding of percentage decrease

I can decrease an amount by a given percentage.

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Lesson details

Key learning points

  1. In all of these representations a single multiplier can be used to find a percentage decrease.
  2. Representation can help when you are not using a calculator.
  3. A multiplier is significantly faster when using a calculator.
  4. To decrease you are going below the original amount.

Keywords

  • Proportion - 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

When using multipliers, pupils can mistake a decimal for the percentage decrease. e.g. 0.52 is a 52% decrease, rather than recognising a 48% decrease

Reminding students that a decimal multiplier greater than 1 means an increase, and a decimal multiplier less than 1 means a decrease. The latter requires a subtraction from 1 or 100%

To embed the fact 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. Conversely, when an answer is 0.52, this says it is a decrease of 48% of 52% of an amount.
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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6 Questions

Q1.
Increase 600 by 5%
Correct Answer: 630
Q2.
Write 62 as a percentage of 200
Correct Answer: 31, 31%
Q3.
Increase 90 by 11%
Correct Answer: 99.9
Q4.
Find 11% of 700
Correct Answer: 77
Q5.
Write 50 as a percentage of 1250
Correct Answer: 4, 4%
Q6.
Find 90% of 625
Correct Answer: 562.5

6 Questions

Q1.
Which statement is the equivalent of "Decrease 50 by 20%"?
Work out 20% of 50
Correct answer: Work out 80% of 50
Divide 50 by 20
Q2.
Which statement is the equivalent of "Increase 130 by 15%"?
Correct answer: Work out 115% of 130
Work out 85% of 130
Work out 15% of 130
Q3.
Which statement is the equivalent of "Decrease 700 by 35%"?
Work out 35% of 700
Correct answer: Work out 65% of 700
Work out 85% of 700
Q4.
Decrease 700 by 4.5%
Correct Answer: 668.5
Q5.
Increase 700 by 4.5%
Correct Answer: 731.5
Q6.
Increase 700 by 18%
Correct Answer: 826