6 methods · 24 worked questions using these methods
★ Signature method unlocked: the technique this chapter rewards most often, with 3 worked questions.
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Treat every percentage change as a decimal multiplier and multiply them together. Never add or subtract percentage rates directly, as each percentage is taken of a new base.
Trigger: A quantity undergoes multiple percentage changes in sequence, or a rate is applied repeatedly over time.
Instances: (i) Increase of r% : multiply by 1+100r; (ii) Decrease of r% : multiply by 1−100r; (iii) Compound changes: multiply the factors, e.g. +25% then −40% is 1.25×0.60.
