Appendix 3: Quantitative skills — Edexcel A-Level Economics A
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Appendix 3: Quantitative skills explained
This skill covers three linked operations used throughout A-Level Economics data questions.
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A percentage expresses a value as a fraction of 100, so 0.25 of a market equals 25%. A percentage change compares a new value with an original value using (new − original) ÷ original × 100; for example, if a price rises from £40 to £50, the change is (50 − 40) ÷ 40 × 100 = 25%. A percentage point change instead subtracts one percentage from another, so an interest rate moving from 3% to 5% rises by 2 percentage points, not 2%. Confusing these two is the central trap: the same move is a 2 percentage point rise but a 66.7% increase. You must also reverse the process, finding an original value from a percentage change, and interpret percentages embedded in tables, index numbers and elasticities.
Your focus
- Calculate a percentage of a given quantity accurately.
- Calculate a percentage change using the original value as the denominator.
- Distinguish and calculate percentage point changes between two percentages.
Show all 4 objectives
- Interpret percentage and percentage point data in economic contexts.
Appendix 3: Quantitative skills exam tips
Marking Points
- Percentage: a value expressed as a proportion of 100, calculated as (part ÷ whole) × 100, e.g. 15 of 60 = 25%.
- Percentage change: (new value − original value) ÷ original value × 100, always dividing by the original, not the new, value.
- Percentage point change: the arithmetic difference between two percentages, e.g. 7% − 4% = 3 percentage points.
- Distinguishing a change in a percentage (percentage points) from a percentage change in that percentage (a relative change).
- Reversing a percentage change to recover an original value, e.g. a value that rose 20% to 120 had an original of 120 ÷ 1.20 = 100.
- Applying percentages to economic data such as inflation, unemployment, interest rates, tax rates and growth rates.
Examiner Tips
- 💡Underline whether the question asks for a percentage change or a percentage point change before calculating.
- 💡Write the formula (new − original) ÷ original × 100 explicitly so the marker can follow your method.
- 💡Sanity-check the sign and size: a fall should give a negative percentage change, and small absolute moves in low percentages can be large relative changes.
Common Mistakes
- Dividing by the new value instead of the original when finding a percentage change; the correction is always to divide the difference by the original value.
- Treating a rise from 3% to 5% as a 2% increase; the correction is that it is a 2 percentage point rise, which is a 66.7% relative increase.
- Adding or subtracting percentages directly when compounding is involved, e.g. assuming two successive 10% rises give 20%; the correction is 1.10 × 1.10 = 1.21, a 21% rise.
- Forgetting to multiply by 100 and leaving the answer as a decimal fraction, so 0.25 is reported instead of 25%.