GCSE›Edexcel GCSE Maths›Mind mapsPercentage and GrowthEdexcel GCSE Maths: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsMultipliersPercentage change is a multiplicative relationship£80 to £100 is 10080=1.25\frac{100}{80} = 1.2580100=1.251.25 for +25%, 0.90 for −10%Apply the multiplier directlyDirect proportiony=kxy = kxy=kx with constant kFind k from one known pair4 litres cost £6, so k=1.5k = 1.5k=1.510 litres cost £15Other proportiony=kx2y = kx^2y=kx2: growth speeds upy=kxy = k\sqrt{x}y=kx: growth slows downy=kxy = \frac{k}{x}y=xk: inverse proportion, y falls as x risesSubstitute a known pair to find kPercentage growthmultipliers and proportion×1.25×0.9Over 100%A as a fraction of B is A÷BA \div BA÷B120 as a fraction of 80 is 150%Over 100% means the new value is biggerMulti-stepConvert everything to decimalsApply each step in order+20% then −10%: 1.20×0.90=1.081.20 \times 0.90 = 1.081.20×0.90=1.08Overall +8%, not +10%Exam tipsMultiply multipliers, never add percentagesIncrease then equal decrease does not return to startCheck the type of proportion in the questionCheck the answer makes sense in context