Circle graph
A circle graph (also called a pie chart) is a circular diagram where each sector represents a proportion of a whole. Circle graphs are commonly used to show budget breakdowns or how a total is divided into parts. To create or interpret a sector, calculate its percentage of 360 degrees — since a full circle is 360°. For example, a section representing 20% of the total covers 20% × 360° = 72°. This visual tool makes proportions easy to compare at a glance and is covered in Saxon Math, Course 2, as part of 7th grade data analysis and statistics.
Key Concepts
Property A circle graph (or pie graph) is commonly used to show components of a budget. To make a sector, calculate its percentage of $360^{\circ}$. $$ 20\% \text{ of } 360^{\circ} = 0.2 \times 360^{\circ} = 72^{\circ} $$.
Examples A survey of favorite pets: 50% Dogs, 25% Cats, 15% Fish, 10% Other. The 'Dogs' sector would be a $180^{\circ}$ angle, taking up half the circle. A student's daily schedule: Sleep (40%), School (25%), Homework (10%), Other (25%). The angle for Sleep is $0.40 \times 360^{\circ} = 144^{\circ}$. A class fundraiser of 500 dollars. Bake sale: 250 dollars (50%), Car wash: 150 dollars (30%), Donations: 100 dollars (20%).
Explanation A circle graph is like slicing up a pizza, where each slice represents a category. The whole pizza is 100 percent of your data, like your monthly allowance. Bigger slices mean bigger percentages! It’s perfect for showing how a whole is divided, like how you spend your time in a day or what types of music your friends prefer.
Common Questions
What is a circle graph (pie chart)?
A circle graph or pie chart is a circular diagram divided into sectors, where each sector represents a proportion of the whole. It’s commonly used to show percentages of a budget, survey results, or data breakdown.
How do you calculate the angle of a sector in a pie chart?
Multiply the percentage by 360 degrees. For example, if a category represents 25% of the total: 0.25 × 360° = 90°.
Why does a circle represent 100% or a whole?
A complete circle spans 360 degrees and represents the entire dataset (100%). Each sector is a fraction of that total, so the angle of each sector is proportional to its percentage of the whole.
How do you read a circle graph?
Look at each sector’s size and label. The largest sector represents the biggest proportion; the smallest represents the smallest. Add all percentages to verify they sum to 100%.
What is the difference between a circle graph and a bar graph?
A circle graph shows parts of a whole (proportional relationships). A bar graph compares separate categories or values. Use a circle graph when you want to show how a total is divided; use a bar graph when comparing different quantities.
When do students learn about circle graphs?
Circle graphs are introduced in 7th grade math as part of data analysis and statistics.
Which textbook covers circle graphs?
Saxon Math, Course 2 covers circle graphs and how to calculate sector angles.