Percentages & Financial Maths — Year 8 Revision Notes
These notes cover finding percentages of amounts, increasing and decreasing by a percentage, percentage change and simple financial problems — all at Year 8 (Stage 8) level.
Finding a percentage of an amount
To find a percentage of an amount, write the percentage as a fraction or decimal and multiply. 25% of 60 = 0.25 × 60 = 15. Useful building blocks are 10% (divide by 10), 1% (divide by 100) and 50% (halve), which you can combine for trickier percentages.
Key Facts & Formulas
- 25% of 60 = 0.25 × 60 = 15
- 10% = ÷ 10
- 1% = ÷ 100
Tips
- Turn the percentage into a decimal before multiplying.
- Build up awkward percentages from 10% and 1%.
Percentage increase and decrease
To increase by a percentage, find the percentage and add it on; to decrease, subtract it. A faster way uses a multiplier: a 15% increase means × 1.15, and a 20% decrease means × 0.80. Multipliers make repeated changes much quicker.
Key Facts & Formulas
- Increase by 15% → × 1.15
- Decrease by 20% → × 0.80
Tips
- For an increase the multiplier is more than 1; for a decrease it is less than 1.
- Decide whether to add or subtract before you start.
Percentage change and financial problems
The percentage change between two values is the actual change divided by the original, times 100. This is how discounts, profit and loss, and simple interest are worked out. Simple interest earned is the percentage rate of the amount, for each year it is invested.
Key Facts & Formulas
- Percentage change = (change ÷ original) × 100
- Simple interest = (rate% of amount) × years
Tips
- Always divide by the original amount, not the new one.
- Read carefully whether a value has gone up or down.
Revision Checklist
- I can find a percentage of an amount
- I can increase or decrease an amount by a percentage
- I can express one quantity as a percentage of another
- I can calculate a percentage change and solve simple financial problems
Frequently Asked Questions
What is a multiplier and why is it useful?
A multiplier is a single number you multiply by to change an amount by a percentage. A 15% increase is × 1.15 and a 20% decrease is × 0.80. Multipliers save time, especially when a change happens more than once.
Build strong foundations in Percentages & Financial Maths
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