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**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.

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**. 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.

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**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.

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**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.

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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.

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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.

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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.

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**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

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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.

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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.

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