New
New
Year 10
Higher

Checking and securing understanding of percentage decrease

I can decrease an amount by a given percentage.

New
New
Year 10
Higher

Checking and securing understanding of percentage decrease

I can decrease an amount by a given percentage.

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.

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%

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.

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).

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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