1. Circle Graphs
and Percents

2. Circle Graphs and Percents
You’ll have seen circle graphs before in earlier grades.
They’re often used to compare different percents.
Circle graphs are useful because they show clearly how the size of one group relates to another.

3. Circle Graphs and Percents
100% is Equal to the Whole Amount
100% of something is all of it.
It’s important to remember this when you’re looking at questions about percents.

4. Circle Graphs and Percents
Example 1
Yesenia has a number of marbles. 65% of the marbles are red. The rest are all blue. What percent of Yesenia’s marbles are blue?
Solution
All the marbles are either red or blue.
percent of red marbles + percent of blue marbles = all marbles
65% + percent of blue marbles = 100%
percent of blue marbles = 100% – 65%
= 35%
So 35% of Yesenia’s marbles are blue.
Solution follows…

5. Circle Graphs and Percents
Circle Graphs Are Often Divided into Percents
Circle graphs show how a total splits into different parts.
This graph represents a math class split into boys and girls.
The whole circle represents the whole class.
The two sections represent the boys and the girls.
The girls section is larger.
This means the class has more girls than boys.

6. Circle Graphs and Percents
When a circle graph shows percents, the whole circle represents 100%.
100%
50%
25%
A section that represents a certain percent fills that percent of the circle.

7. Circle Graphs and Percents
Example 2
This circle graph shows the results of a survey to find which out of apples, bananas, and oranges students liked best.
What percent of the students like bananas best?
Solution
The whole circle represents 100%, so the total value of all the sections must be 100%.
Call the percent of students who like bananas best b%.
Then b = 100
The total of all sections is 100%
60 + b = 100
= 60
b = 100 – 60 = 40
Subtract 60 from both sides
So 40% of the students like bananas best.
Solution follows…

8. Circle Graphs and Percents
Guided Practice
In Exercises 7–10, find the missing value in each circle graph. 7. 8.
100% – 50% = 50%
100% – ( )% = 15% 9.
10.
100% – ( )% = 45%
100% – ( )% = 26%
Solution follows…

9. Circle Graphs and Percents
Guided Practice
A survey asked people which of three drinks they prefer. This graph shows the number of people who said they prefer each drink.
11. How many people answered the survey?
= 50 people
12. What fraction of these people preferred each drink?
Water: , Juice: , Milk: = 10 50 1 5 20 2
13. What percent of these people preferred each drink?
Water: (1 ÷ 5) × 100 = 20%, Juice: (2 ÷ 5) × 100 = 40%, Milk: (2 ÷ 5) × 100 = 40%
Solution follows…

10. Circle Graphs and Percents
Guided Practice
This graph shows the number of insects a scientist counted for a study.
14. How many insects were there in total?
= 500 insects
15. What percent of each type of insect were there?
Crickets: (125 ÷ 500) × 100 = 25%, Wasps: (75 ÷ 500) × 100 = 15%, Bees: (125 ÷ 500) × 100 = 25%, Butterflies: (175 ÷ 500) × 100 = 35%
Solution follows…

11. Circle Graphs and Percents
You Can Turn Percents on Circle Graphs into Numbers
If you know how many units make up the full 100% of a circle graph, then you can work out how many each section represents.
50%
25%
If this graph represents 200 people…
…then 100% = 200 people…
…so 25% = 50 people

12. Circle Graphs and Percents
Example 3
Chris, Martina, and D’Andre each ran for student body president. A total of 150 students voted in the election, and the outcome of the election is shown in the circle graph. How many students voted for Martina?
Solution
The circle graph tells you 40% of the students voted for Martina. You know that the whole circle graph represents 150 students.
So the number of students who voted for Martina is
40% of 150 = 0.4 × 150 = 60
A total of 60 students voted for Martina.
Solution follows…

13. Circle Graphs and Percents
Round Up
Circle graphs are useful for giving out information.
People who don’t know much about math can still understand what it means when one part of the circle is bigger than another.

14. Circle graphs

15. Circle graphs

16. Use a circle graph to organize data