Rullst AcademyRullst Academy/Lesson
Mathematics: relationships for creating · Lesson 06 / 08

Charts that tell the whole story

For eight lanterns, A uses 28 tokens and B uses 32. One bar looks much larger when the scale starts at 27. The picture needs context.

Learning paths8 min

Let's discover together

  1. 1

    A bar chart uses lengths to represent quantities. When comparing lengths, starting at zero and using the same scale helps preserve that relationship.

  2. 2

    With an origin of 27, the drawn part of 28 has length 1 and that of 32 has length 5. This does not mean 32 is five times 28.

  3. 3

    The real difference is 32 − 28 = 4 tokens. Twice 28 would be 56. Read numbers and units; do not rely only on the visual impression.

  4. 4

    Other chart types may use cropped scales to study small changes if clearly explained. In this workshop, bars start at zero and come with an accessible table.

  5. 5

    Also check when, how and from which cases the data was obtained. A table can have correct calculations yet fail to represent the question you want to answer. Our values come from a fictional model, not a survey of people.

✦
YOUR MISSION

Read values, units, origin and scale before comparing bars.

Now it's your turn

Discovery workshop

Read beyond the height

Values: A = 28 tokens; B = 32 tokens.

Zero origin

0204060AB2832

Origin at 27: notice the cropped scale

27293133AB2832

Both drawings represent A = 28 and B = 32 tokens. Only the scale changed. The difference is still 4 tokens.

Build your answers and check when you are ready.
A moment to understand

The bars suggest B is twice A. Which check helps?

I need a hint

The drawn length depends on where the scale starts.

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Take it with you

Sketch bars for 28 and 32 starting at zero. Then describe the comparison in text for someone who cannot see the chart.

At your own pace

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