Rates of ChangeAQA GCSE Maths: Flashcards

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What does it mean for $X$ to be inversely proportional to $Y$?

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What does it mean for $X$ to be inversely proportional to $Y$ ?: $X$ is proportional to $\frac{1}{Y}$ , so $X = \frac{k}{Y}$ for some constant $k$ .
What does the gradient of a straight-line graph represent?: A constant rate of change.
How do you find the instantaneous rate of change on a curve?: Draw a tangent at the point and calculate its gradient.
Give the formula for density.: Density = mass ÷ volume.
Give the formula for pressure.: Pressure = force ÷ area.
Give the formula for speed.: Speed = distance ÷ time.
What is a compound unit?: A unit made up of two or more measures, such as speed, density or pressure.
How do you convert km/h to m/s?: Convert both parts: multiply by 1000 to change km to m, and divide by 3600 to change hours to seconds (i.e. multiply the km/h value by $\frac{1000}{3600}$ ).
How do you use an exchange rate to convert currency?: Multiply the amount by the exchange rate for the currency you are converting to.
What is a rate of pay?: A compound unit describing how much someone is paid per unit of time (e.g. £ per hour).
If $X$ is directly proportional to $Y$ and $X = 12$ when $Y = 4$ , find the constant of proportionality $k$ .: $k = X \div Y = 12 \div 4 = 3$