Compound bar charts · Usually met around P5
Compound bar charts
Read the key, then the scale.
How to do it
Method
Read the key, then the scale
Each line 2: 8 × 2 = 16, 6 × 2 = 12, 16 − 12 = 4
Another way
Count lines first
8 − 6 = 2, 2 × 2 = 4
In full
A compound bar chart puts two sets of data side by side, with two bars for each item. First read the key to see which colour is which set. Then see what each grid line stands for (it isn't always 1). Each line is 2, and the bar reaches the 8th line: 8 × 2 = 16. To compare an item's two bars: 4A has 16 girls and 12 boys, 16 − 12 = 4, so 4 more girls. To compare one set across two items, such as the boys in 4A and 4C, take one away from the other in the same way. For a set's total, add its bars one by one. Quicker: count grid lines, and only multiply at the end: girls 8 lines, boys 6, 8 − 6 = 2, so 2 lines apart, 2 × 2 = 4.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Adults in Mar: ? people
Show the answer and working
Answer: Adults in Mar: 70000 people
Key: the left bars are children, the right adults; each grid line stands for 10000. Mar, adults: line 7, 7 × 10000 = 70000
Example 2
Red: girls − boys = ?
Show the answer and working
Answer: Red: girls − boys = 8
Key: the left bars are boys, the right girls; each grid line stands for 2. Red: boys: line 3, 3 × 2 = 6; girls: line 7, 7 × 2 = 14; 14 − 6 = 8
Example 3
4C in all: ? pupils
Show the answer and working
Answer: 4C in all: 14 pupils
Key: the left bars are boys, the right girls; each grid line stands for 2. 4C: boys: line 1, 1 × 2 = 2; girls: line 6, 6 × 2 = 12; 2 + 12 = 14
Practise it in the game →Compound bar charts · Free to start, unlimited questions, no download