GCSE Maths (Edexcel)

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Deriving Direct Proportionality Equations

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Ratio, Proportion and Rates of Change Ratio, Proportion and Rates of Change

Deriving Direct Proportionality Equations

5:21 Direct Proportionality
Spec R13
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  • Direct proportionality means that two quantities are related in such a way that if one quantity is multiplied by a certain number, the other quantity is also multiplied by the same number.
  • The constant of proportionality, denoted as k, is the number that links the two quantities in a direct proportion.
  • The equation for direct proportionality can be written as y = kx or x = ky, where y and x are the two quantities.
  • To find the constant of proportionality, substitute known values of x and y into the equation and solve for k.
  • The constant of proportionality can be a whole number, fraction, or decimal.
  • Being able to derive equations of proportionality is useful in various fields such as mathematics, physics, and other sciences.
  • In the given example, the variables m and n are directly proportional. When m = 16, n = 40. The equation linking m and n is m = 0.4n.
  • In another example, the time it takes to boil a kettle (t) is directly proportional to the volume of water in it (v). The equation showing the relation between t and v is v = (50/3)t.

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