Compound bar charts · Usually met around P5
Compound bar charts: big scales and drawing one
Key first, then what a line stands for.
How to do it
Method
Key first, then what a line stands for
Top at line 3, a line is 2,000: 3 × 2,000 = 6,000
Another way
Count the gap first
2 lines apart: 2 × 2,000 = 4,000
In full
Read the key first to tell the two sets of bars apart, then see what each line on the side axis stands for (1,000, 10,000, 100,000…). To read a bar: count the lines up to its top and multiply by what a line stands for; a top halfway between two lines adds half a line. To compare two bars in a month, subtract the two values, or count the lines between them first and multiply. To draw a chart, find the biggest value and choose a scale that keeps the longest bar on the axis but as long as possible; round values that don't fall on a line first.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
The chart shows the takings (in dollars) of Shop A and Shop B over four months. How many dollars apart were the two shops in July?
Show the answer and working
Answer: 45000 dollars
In July Shop B's bar stops halfway between lines: 6.5 lines, 6.5 × 10,000. Count the gap in lines, then multiply: 45,000 dollars.
Example 2
The chart shows a city's visitors in four months, last year and this year. How many visitors came in these four months this year?
Show the answer and working
Answer: 2100000 visitors
Only this year's four bars: 21 lines in all, 100,000 each: 21 × 100,000 = 2,100,000.
Example 3
Drawing a bar chart, each line stands for 1,000 people. One month had 9,215 people. Rounded to the nearest thousand first, how many lines high should its bar be?
Show the answer and working
Answer: 9 lines
The hundreds digit is 2, so to the nearest thousand it is about 9 thousands: 9 lines.
Practise it in the game →Compound bar charts · Free to start, unlimited questions, no download