GCSE Maths (Edexcel)

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Direct Proportionality Graphs

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

Direct Proportionality Graphs

2:33 Direct Proportionality
Spec R10 R14
Previous Deriving Direct Proportionality Equations Next Proportionality in Ratios
  • The graph relating two proportional variables will be a straight line through the origin.
  • The equation for a proportional relationship is y = kx + 0.
  • The equation of a straight line is y = mx + c, where m is the gradient and c is the y intercept.
  • It is important to be familiar with this relationship for exams and science subjects.
  • The graph shows a directly proportional relationship between the mass of a loaf of bread and its calorie content.
  • To calculate the calorie content of a 400 gram loaf of bread, divide 400 by 500 to get 0.8.
  • Multiply the calorie content of 1,300 by 0.8 to get the required calorie content of 1,040 kilocalories.

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