In these lessons, we will learn:

- how to construct circle graphs or pie charts
- how to read or use circle graphs or pie charts

A **pie chart** (also called a Pie Graph or Circle Graph) makes use of sectors in a circle. The angle of a sector is proportional to the frequency of the data.

The formula to determine the angle of a sector in a circle graph is:

Study the following steps of constructing a circle graph or pie chart:

** Step 1**: Calculate the angle of each sector, using the formula

* Example: *

In a school, there are 750 students in Year1, 420 students in Year 2 and 630 students in Year 3. Draw a circle graph to represent the numbers of students in these groups.

* Solution: *

Total number of students = 750 + 420 + 630 = 1,800.

Draw the circle, measure in each sector. Label each sector and the pie chart.

Steps to making a circle graph

1. Determine what percent of the data is from each category.

2. Determine what percent of 360 degrees represents each category.

3. Divide up the circle.

This video shows how to construct a circle graph from the given data.

This video shows how to draw a pie chart by working out angles from a table.

Example: The table shows 18 people's favorite color. Display the information as a pie chart.

We could also use a given circle graph to answer some questions about the data.

* Example: *

The following pie chart shows a survey of the numbers of cars, buses and motorcycles that passes a particular junction. There were 150 buses in the survey.

a) What fraction of the vehicles were motorcycles?

b) What percentage of vehicles passing by the junction were cars?

c) Calculate the total number of vehicles in the survey.

d) How many cars were in the survey?

* Solution: *

a) Fraction of motorcycles

b) To convert the angle of a sector into a percentage, we use the formula:

Percentage

Percentage of cars

c) Let *x* be the total number of vehicles

The total number of vehicles is 1,800

d) Number of cars

Example: For the past year, a travel agency has collected data about the number of individual tickets that it sells for its signature product: a Mediterranean Cruise. The monthly data on ticket sales is shown below. What are the best and worst months for cruise sales?

Use the circle graph below to determine what percent of people prefer either soccer or football.

Rotate to landscape screen format on a mobile phone or small tablet to use the **Mathway** widget, a free math problem solver that **answers your questions with step-by-step explanations**.

You can use the free Mathway calculator and problem solver below to practice Algebra or other math topics. Try the given examples, or type in your own problem and check your answer with the step-by-step explanations.

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