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Statistics & Probability · Foundation & Higher

Bar charts & pictograms

Bar charts and pictograms are ways to display categorical or discrete data. You need to draw them accurately and use them to read off and compare data values.

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Key facts to remember

  • 1In a bar chart, the height (or length) of each bar represents the frequency.
  • 2Bars in a bar chart should be equal width with gaps between them (for discrete data).
  • 3A dual bar chart compares two data sets side by side.
  • 4In a pictogram, each symbol represents a fixed number of items — use the key.
  • 5Half a symbol in a pictogram represents half the key value.
  • 6Frequency density is not used for bar charts — only for histograms.
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Worked examples

Example 1

A pictogram uses ★ = 4 students. A subject has 3½ stars. How many students chose it?

Working

  1. Each star = 4 students
  2. 3½ stars = 3.5 × 4 = 14 students
Answer14 students
Example 2

A bar chart shows 40 students chose maths, 25 chose English, 35 chose science. What fraction chose science?

Working

  1. Total = 40 + 25 + 35 = 100
  2. Fraction for science = 35/100 = 7/20
Answer7/20
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Common mistakes

✗Drawing bars of unequal width in a bar chart.
✗Misreading the pictogram key — always check how many each symbol represents.
✗Joining the tops of bars with lines (this turns it into a line graph, which is for continuous data).
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Exam tips

✓Always label both axes clearly with a title and units.
✓For pictograms, use a ruler to draw symbols of consistent size and check the key carefully.

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