MA19-05 Maths Coming soon
Reverse percentages: find the original value
MA19-05
This lesson is coming soon.
In this lesson
Find the original value before a percentage change was applied, by dividing the changed value by the correct decimal multiplier, explicitly contrasted against finding a new value.
What it covers
- Recognising a reverse-percentage problem (given a changed value, find the original)
- Building the correct decimal multiplier from the stated percentage change (recapped as a known result)
- Dividing the changed value by that multiplier to find the original
- Explicit contrast against 'find the new value' (multiply) so the two directions are never confused
Key words
For: AQA GCSE 8300, Cambridge IGCSE 0580, Edexcel GCSE 1MA1, Edexcel IGCSE 4MA1, Eduqas GCSE C300, OCR GCSE J560
On the specification
| Board | Spec | Statement |
|---|---|---|
| AQA GCSE 8300 | R9 | Define percentage as ‘number of parts per hundred’ |
| Cambridge IGCSE 0580 | E1.13 | Calculate a given percentage of a quantity. |
| Edexcel GCSE 1MA1 | R9 | Define percentage as ‘number of parts per hundred’; interpret percentages and percentage changes as a fraction or a decimal, and interpret these multiplicatively; express one quantity as a percentage of another; compare two quantities using percentages; work with percentages greater than 100%; solve problems involving percentage change, including percentage increase/decrease and original value problems, and simple interest including in financial mathematics |
| Edexcel IGCSE 4MA1 | F1.6F | Use reverse percentages |
| Eduqas GCSE C300 | FR10 | Define percentage as 'number of parts per hundred'; interpret percentages and percentage changes as a fraction or a decimal, and interpret these multiplicatively; express one quantity as a percentage of another; compare two quantities using percentages; work with percentages greater than 100%; solve problems involving percentage change, including percentage increase / decrease and original value problems, and simple interest including in financial mathematics |
| Eduqas GCSE C300 | HR10 | Define percentage as 'number of parts per hundred'; interpret percentages and percentage changes as a fraction or a decimal, and interpret these multiplicatively; express one quantity as a percentage of another; compare two quantities using percentages; work with percentages greater than 100%; solve problems involving percentage change, including percentage increase / decrease and original value problems, and simple interest including in financial mathematics |
| OCR GCSE J560 | 2.03c | Increase or decrease a quantity by a simple percentage, including simple decimal or fractional multipliers. Apply this to simple original value problems and simple interest. |
For teachers
This GCSE Maths lesson teaches reverse percentages: find the original value. By the end, students should be able to find the original value before a percentage change was applied, by dividing the changed value by the correct decimal multiplier, explicitly contrasted against finding a new value. It works through three worked examples and the mistakes examiners report.