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**SPI: 0606.4.4 Calculate with circumferences and areas of circles.**

6th Grade SPI: Calculate with circumferences and areas of circles.

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**The circumference of a circle is**

The distance around a circle Hint: Circumference remember circle around

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**First we must define some things about a circle.**

The radius is the distance from the center of a circle to any point on a circle. Hint: I like to define it as halfway through!

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**The diameter is the distance across a circle through the center.**

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**We use Pi as the measurement to help us find the circumference of a circle.**

Pi, not Pie!

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HINT: Pi =3.14

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**Two formulas are used in finding the circumference of a circle.**

WHEN THE CIRCLE HAS A DIAMETER MEASUREMENT, USE THE FOLLOWING FORMULA. Circumference = d 4in. 3.14 x 4in. 12.6in.

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**HINT: Always round your answers to the nearest tenth.**

When the radius of a circle is given, the following formula should be used. Circumference = 2 r 2 x 3.14 x 5cm 31.4cm HINT: Always round your answers to the nearest tenth.

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**Tell me what formula would be used to solve the next five problems.**

NOW…Let’s have some fun. Tell me what formula would be used to solve the next five problems.

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3in C = 2 x 3.14 x r

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8ft C = 3.14 d

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122mm C = 2 x 3.14 x d

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17.5 cm C = 3.14 x d

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122.5mm C = 2 x 3.14 x r

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**Now that we have determined the correct formula for each, let’s work the problems.**

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The answer is: 18.8in 3in C = 2 x 3.14 x r

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8ft C = 3.14 d The answer is: 25.1ft

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122mm C = 2 x 3.14 x d The answer is: mm

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17.5 cm C = 3.14 x d The answer is: 55cm

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122.5mm C = 2 x 3.14 x r The answer is: 76,930mm

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