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Calculating the range

Statistics · Grade 7–9

Strand: Statistics Substrand: Averages and range Sparx code: U526 Sparx levels: 1, 2

Key steps (method)

  • Identify what statistic/graph the question is asking for.
  • Organise the data (frequency table if needed) and total the frequencies.
  • Apply the correct method: mean = sum(f×x)/sum(f), median from ordered positions, etc.
  • Read graphs carefully using the scales (including class boundaries for grouped data).
  • State the answer clearly, with appropriate rounding.

Common mistakes

  • Using midpoints incorrectly for grouped data.
  • Reading the wrong scale or misreading class boundaries.
  • Forgetting to divide by total frequency when finding the mean.
  • Mixing up correlation with causation in interpretations.

Quick notes

  • If you get stuck, try a simpler version of the problem first or plug in easy numbers to test your method.
  • For multi-step questions, label each step and keep intermediate results.
  • For exam questions, always aim to make your work “mark-scheme readable”.

Self-assessment

  • Can I define it? Write a one-sentence definition of Calculating the range (or the key term in the question).
  • Can I do it? Do 3 questions: one easy, one standard, one harder. Don’t look at notes until you’ve tried.
  • Can I explain it? In 2–3 sentences, explain why the method works (or what would go wrong with a common mistake).
  • Can I check it? State one quick check (estimate, units, sign, reasonableness).

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Notes