1. Using Radius to Find Circumference
EXAMPLE 1
Using Radius to Find Circumference
Find the circumference of a circle with a radius of 11 meters.
SOLUTION
C = 2πr
Circumference formula
2(3.14)(11)
Substitute 3.14 for π and 11 for r.
= 69.08
Multiply.
ANSWER
The circumference is about meters.

2. . 213 EXAMPLE 2 Using Diameter to Find Circumference
Find the circumference of the circle.
SOLUTION
The measure shown is a diameter, so use the circumference formula that involves the diameter.
C = πd
Circumference formula
22 71
. 213
Substitute. Use for π because 21 is divisible by 7.
22 7
= 66
Multiply
ANSWER
The circumference is about 66 feet.

3. Standardized Test Practice
EXAMPLE 3
Standardized Test Practice
SOLUTION
You are asked to find the diameter, so use the circumference formula that involves diameter.
C = πd
Circumference formula d
Substitute for C and 3.14 for π. =
3.14d
Divide each side by 3.14.
135 = d
Simplify.
ANSWER
The diameter is about 135 feet. The correct answer is C.

4. Use for π because 28 is divisible by 7. ANSWER
GUIDED PRACTICE
for Examples 1, 2, and 3
Find the circumference of the circle. Use 3.14 or for π . Explain your choice of π .
22 7 1.
Use for π because 28 is divisible by 7.
ANSWER
The circumference is about 176 mi.

5. GUIDED PRACTICE
for Examples 1, 2, and 3
Find the circumference of the circle. Use 3.14 or for π . Explain your choice of π .
22 7 2.
Use 3.14 for π because 9.5 is not divisible by 7.
ANSWER
The circumference is about m.

6. GUIDED PRACTICE
for Examples 1, 2, and 3
Find the circumference of the circle. Use 3.14 or for π . Explain your choice of π .
22 7 3.
Use 3.14 for π because 16 is not divisible by 7.
ANSWER
The circumference is about cm.

7. GUIDED PRACTICE
for Examples 1, 2, and 3
4. diameter = 32 in.
Use 3.14 for π because 32 is not divisible by 7.
ANSWER
The circumference is about cm.

8. The circumference is about 440 ft.
GUIDED PRACTICE
for Examples 1, 2, and 3
5. diameter = 140 ft.
ANSWER
The circumference is about 440 ft.
Use for π because 140 is divisible by 7. 22 7

9. GUIDED PRACTICE
for Examples 1, 2, and 3
6. radius = 1.5 km
Use 3.14 for π because 1.5 is not divisible by 7.
ANSWER
The circumference is about 9.42 cm.

10. GUIDED PRACTICE
for Examples 1, 2, and 3
7. What If? In Example 3, suppose the circumference of the Ferris wheel is 462 feet. What is the diameter of the Ferris wheel?
ANSWER
The diameter is about 147 feet.