GCSE›Edexcel GCSE Maths›Mind mapsCompound MeasuresEdexcel GCSE Maths: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhat are they?Two units combined into one rateFormed by dividing one quantity by anotherThe unit tells you the formulakm/h means distance ÷ timeSpeedspeed=distancetime\text{speed} = \frac{\text{distance}}{\text{time}}speed=timedistancedistance=speed×time\text{distance} = \text{speed} \times \text{time}distance=speed×time150 km in 3 hours gives 50 km/hConvert minutes to hours firstDensitydensity=massvolume\text{density} = \frac{\text{mass}}{\text{volume}}density=volumemass45 g in 9 cm³ gives 5 g/cm³Find the volume first for cubes and cylindersCube side 2 cm, 8 g/cm³ gives 64 gCompound measuresspeed, density, pressurem/sg/cm³N/m²Pressurepressure=forcearea\text{pressure} = \frac{\text{force}}{\text{area}}pressure=areaforceforce=pressure×area\text{force} = \text{pressure} \times \text{area}force=pressure×areaUnits: N/m² or PaRatesUnit price is cost per item or kg5 kg for £4.50 gives £0.90 per kgPay rate is earnings per hourCompare offers using the same unitExam tipsMake units match before you calculateNever divide km by minutesRearrange the formula to find the other quantities