GCSE Maths (Edexcel)

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Direct Proportionality

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

Direct Proportionality

6:29 Direct Proportionality
Spec R10 R13
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  • Direct proportionality: two quantities are directly proportional if increasing one by a multiple will cause the other to also increase by that multiple
  • Example of direct proportionality: small rock and large rock with different volumes and masses
  • Direct proportionality is useful in math and science
  • Example problem: Bella buys 5 batteries for 3.50, Eric buys 10 batteries, calculate how much Eric spends
  • Number of batteries bought is directly proportional to the cost
  • Eric bought twice as many batteries as Bella, so he will need to pay twice as much
  • Proportional to symbol is used to indicate two quantities are directly proportional
  • Proportionality can be shown as a relation of the form Y is KX, where K is a constant of proportionality
  • Example problem: time to upload a video is proportional to the length of the video, T is 1.5L
  • Rearrange equation to make L the subject
  • Substitute values to find the length of the video that takes 1 hour to upload: L = 40 seconds

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