Name the base amount
A percentage is always a percentage of something. Identify that original or principal amount before calculating.
CSEC Math LabLearn · practise · master
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14 min
Section 2Consumer Arithmetic
Make every dollar tell the truth
Use percentages and rates to model normal business and personal finance decisions.
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Learn the idea
Three things to notice
A multiplier is faster
After a 15% discount, 85% remains. Multiply by 0.85 rather than subtracting in two separate calculations.
Track the time unit
Interest rates are usually annual. Convert months to years before using I = PRT.
Do not memorise the words alone. The worked example shows how to choose and apply the idea.
Syllabus coverage
Profit and lossDiscountsHire purchaseSimple and compound interestDepreciationExchange rates