Measurement and Data
Bar graphs with scales
Read values off a bar graph whose scale counts in steps of more than one, and choose a sensible scale of your own.
A bar graph turns numbers into heights so they can be compared at a glance. The scale up the side is what turns a height back into a number, so it is the first thing to read and the easiest thing to forget.
Read the scale first
If each line stands for 5, then a bar three lines tall shows 15, not 3. The same picture means completely different numbers under a different scale.
Worked example
Each line on a graph stands for 4. What does a bar six lines tall show?
Six lines, four each: 6 × 4 = 24.
Counting the lines gives you the number of steps; the scale tells you how big a step is.
Choosing a scale
When you draw your own graph, look at the largest number first. Pick a scale that lets it fit on the page without leaving the small bars squashed flat against the bottom.
Try it together
A bar graph has ten lines above zero, and the largest number to show is 45. Let us choose a scale.
The question is always the same: how much does each line have to stand for?
1.If each line stood for 2, what is the largest number the graph could show?
Have a go
Have a go on your own: each line stands for 10. What does a bar seven lines tall show?
Ready to practice?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.