Interpret sector (pie) graphs
Theory
A sector graph shows a whole group as a circle cut into sectors, so each sector is the fraction of the whole its category takes. Multiply a sector's fraction by the total to find how many it stands for.
A sector graph (or pie graph) shows a whole group as a circle cut into sectors, one for each category.
The whole circle stands for the whole group, so all the sectors together make one whole.
A bigger sector is a bigger fraction and a larger part of the group.
To find how many a sector stands for, multiply its fraction by the total: \(\text{fraction}\times\text{total}\).
Each sector can be read as a fraction and as a number.
| Drink | Fraction | Count (of 24) |
|---|---|---|
| Water | \(\dfrac{1}{2}\) | \(12\) |
| Juice | \(\dfrac{1}{3}\) | \(8\) |
| Milk | \(\dfrac{1}{6}\) | \(4\) |
How to read a sector graph
- Compare the sectors to see which fills the most of the circle.
- Name each sector's fraction of the whole.
- Multiply a fraction by the total to find how many it stands for.
- Check that the fractions add to one whole.
The largest sector fills the most of the circle.
| \(\dfrac{1}{2}>\dfrac{1}{3}>\dfrac{1}{6}\) | Water |
Multiply the fraction by the total.
| \(\dfrac{1}{2}\times 24\) | \(=\) | \(12\) |
Multiply the fraction by the total.
| \(\dfrac{1}{3}\times 24\) | \(=\) | \(8\) |
Add over a common denominator of \(6\).
| \(\dfrac{3}{6}+\dfrac{2}{6}+\dfrac{1}{6}\) | \(=\) | \(1\) |
Common pitfalls
Frequently asked questions
What does the whole circle stand for?
The whole group. Every sector is a part of it, so all the sectors together make one whole.
How do I find how many a sector stands for?
Multiply the sector's fraction by the total. Water is a half of \(24\), so \(\dfrac{1}{2}\times 24 = 12\).
Which sector is the biggest category?
The one that fills the most of the circle. A bigger sector is a bigger fraction and a larger part of the group.
Do the fractions always add to one?
Yes. Because the sectors are the parts of one whole, their fractions add to one, and their counts add to the total.
Can a sector graph show percentages?
Yes. The same sectors can be read as fractions, as percentages that add to \(100\%\), or as numbers of people that add to the total.