Bar graphs: choosing a scale
Pupils counted the vehicles passing their school in an hour: 75 motorbikes, 50 rickshaws, 45 cars, 30 bicycles and 20 buses. Draw the bar graph with different scales and see how many units tall each bar must be.
Core concept
In short: Draw a bar graph where one square stands for many, so big numbers fit.
A scale such as 1 unit = 10 vehicles lets big counts fit on a graph: the height of each bar is the count divided by the scale, and a bar can be part of a unit
Topic: Data handling
A bar graph shows numbers as bars: the taller the bar, the bigger the number. If you counted 75 motorbikes, a bar 75 squares tall would not fit in your notebook. So we choose a scale, such as 1 unit = 10 vehicles. Then 75 motorbikes need a bar 75 ÷ 10 = 7.5 units tall, and 20 buses a bar of 2 units. The same scale must be used for every bar, and it is written on the graph so readers can turn heights back into counts. A small scale makes a tall graph; a big scale makes a short one, but small differences become harder to see.
What you will learn
- Choose a suitable scale for a bar graph.
- Work out the height of each bar from the count and the scale.
- Read a count back from a bar's height and the scale.
Before you start
- Know how to divide by 5, 10 and 25.
Materials
- Squared paper, a ruler and coloured pencils
Equipment
- None
Procedure
- Record the graph with 1 unit = 10 vehicles.
- Change the scale to 1 unit = 5 vehicles and record.
- Change the scale to 1 unit = 25 vehicles and record.
How this simulation is simplified
- Each bar uses the same scale, and heights are measured in grid units.