Finding the original amount after an increase
I can calculate the original value, given the final value after a stated percentage increase.
Finding the original amount after an increase
I can calculate the original value, given the final value after a stated percentage increase.
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Lesson details
Key learning points
- A bar model can be used to find the original amount after a percentage increase
- A double number line can be used to find the original amount after a percentage increase
- A ratio table can be used to find the original amount after a percentage increase
- In all of these representations a single multiplier can be used to find the original amount after a percentage increase
Keywords
Reciprocal - The reciprocal is the multiplicative inverse of any non-zero number. Any non-zero number multiplied by its reciprocal is equal to 1.
Common misconception
A single digit percentage is incorrectly worked out by dividing by 10 and not 100 e.g 3% = 0.3. This error continues when increasing amounts e.g increase 40 by 3% has a multiplier of 1.3
Remind pupils that to covert a percentage into a decimal we divide by 100. This applies with increase too e.g 120% has a multiplier of 1.2
To help you plan your year 8 maths lesson on: Finding the original amount after an increase, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 8 maths lesson on: Finding the original amount after an increase, download all teaching resources for free and adapt to suit your pupils' needs.
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Explore more key stage 3 maths lessons from the Understanding multiplicative relationships: percentages and proportionality unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
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Lesson video
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Prior knowledge starter quiz
6 Questions
1.02
0.98
1.2
0.8