Worked Examples Circumference

Worked Examples: Circle
Circumference

Anthony White
Jen Kershaw

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Jen Kershaw

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Printed: July 12, 2017

www.ck12.org Chapter 1. Worked Examples: Circle Circumference

1CHAPTER Worked Examples: Circle
Circumference

Learning Objectives

In this concept, you will learn to find the circumference of circles given the radius or diameter.

Worked Examples: Circumference of a Circle

Example 1

Tyrone has been hired to build a deck around a circular above-ground pool. Before he starts the project, he needs
to know the circumference of the pool. Tyrone doesn’t have a tape measure long enough to go completely around
the pool, but he knows that the pool is 30 feet across. How can Tyrone use the information that he already knows to
determine the circumference of the pool?
Solution:
The pool’s diameter is 30 feet. The only other thing Tyrone needs to find the circumference of the pool is the equation
relating diameter and circumference.

C = dπ
To find the circumference of the pool, first, substitute the given information into the equation.

C = 30π

Next, substitute 3.14 for pi.

C = 30(3.14)

Then, multiply.

C = 94.2 feet

The pool’s circumference is 94.2 feet.

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Example 2
Find the circumference of a circle with a diameter of 5.5 feet.

Solutin:
First, substitute the given information into the equation.

C = dπ
C = 5.5(3.14)

Next, multiply.

C = 17.27 feet

The answer is 17.27 feet.
Example 3
Find the circumference given the diameter.

d = 5 in

Solution:
First, substitute the given information into the equation.

C = dπ
C = 5(3.14)

Next, multiply.

C = 15.7 inches

The answer is 15.7 inches.

Example 4 r = 3 in
Find the circumference given the radius.

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www.ck12.org Chapter 1. Worked Examples: Circle Circumference

Solution:
First, substitute the given information into the equation.

C = 2rπ
C = 2(3)(3.14)

Next, multiply.

C = 18.84 inches

The answer is 18.84 inches.

Example 5
Find the circumference given the diameter.

d = 2.5 cm

Solution:
First, substitute the given information into the equation.

C = dπ
C = 2.5(3.14)

Next, multiply.

C = 7.85 cm

The answer is 7.85 cm.

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