Ratio, Proportion and Rates of Change

Scheme of work: Key Stage 3: Year 8: Term 3: Ratio, Proportion and Rates of Change

Prerequisite Knowledge

  • Work interchangeably with terminating decimals and their corresponding fractions.
  • Define percentage as the number of parts per hundred, interpret percentages and percentage changes as a fraction or a decimal
  • Interpret fractions and percentages as operators

Key Concepts

  • If the ratio between two things is the same, they are in direct proportion.
  • To divide an amount in a given ratio find the value of one share by finding the total number of shares, then divide the amount by the total number of shares.
  • To compare values work out the cost per unit or number of units per pound or penny.  This takes the form of 1 : n.
  • A common misconception is to write the ratio of 2 : 3 as 2/3.  Emphasise the need to consider the total number of shares when writing a ratio as an equivalent fraction or percentage.

Working Mathematically

  • Develop fluency
    • Consolidate their numerical and mathematical capability from key stage 2 and extend
      their understanding of the number system
    • Select and use appropriate calculation strategies to solve increasingly complex problems.
  • Reason mathematically
    • Extend their understanding of the number system; make connections between number
      relationships, and their algebraic and graphical representations
    • Extend and formalise their knowledge of ratio and proportion in working with measures
      and geometry, and in formulating proportional relations algebraically
  • Solve problems
    • Develop their mathematical knowledge, in part through solving problems and evaluating
      the outcomes, including multi-step problems
    • Select appropriate concepts, methods and techniques to apply to unfamiliar and non-routine problems.

Subject Content

  • Ratio, proportion and rates of change
    • Change freely between related standard units [for example time, length, area, volume/capacity, mass]
    • Use scale factors, scale diagrams and maps
    • Express one quantity as a fraction of another, where the fraction is less than 1 and greater than 1
    • Use ratio notation, including reduction to simplest form
    • Divide a given quantity into two parts in a given part:part or part:whole ratio; express the division of a quantity into two parts as a ratio
    • Understand that a multiplicative relationship between two quantities can be expressed as a ratio or a fraction
    • Relate the language of ratios and the associated calculations to the arithmetic of fractions
    • Solve problems involving direct and inverse proportion, including graphical and algebraic representations
    • Use compound units such as speed, unit pricing and density to solve problems.

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