Data Handling
Reading bar charts
Read a bar chart, use its scale to turn a bar height into a number, and compare the bars.
A bar chart turns a table of numbers into a picture. The tallest bar is the biggest number and the shortest bar is the smallest, and you can see that at a glance without doing any arithmetic at all. What you cannot see at a glance is how much each bar is actually worth — for that you have to read the scale up the side.
Read the scale before you read the bars
One square up the side rarely means one. It might mean 2, or 5, or 10. A bar that is 7 squares tall on a scale of 5 stands for 35, not 7 — so the chart that looks like it says seven is really saying thirty-five. Checking the scale first is the difference between reading a chart and guessing at it.
Worked example
Each square of a scale stands for 5 books. A bar is 7 squares tall. How many books is that?
Count the squares the bar reaches: 7.
That is the height, but not yet the answer.
Try it together
Now let us compare two bars on a scale of 5 together.
One bar is 7 squares tall and another is 4 squares tall. Each square stands for 5 books.
1.How many books does the taller bar stand for?
Have a go
Have a go on your own: each square of a scale stands for 3 cars, and a bar is 6 squares tall. How many cars does it stand for?
Hint: Six lots of three.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.