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7 th Grade Calculate with circumferences and areas of circles.

CIRCUMFERENCE. 7 th Grade Calculate with circumferences and areas of circles. The circumference of a circle is. The distance around a circle. Hint: Circumference remember circle around. First we must define some things about a circle.

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7 th Grade Calculate with circumferences and areas of circles.

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  1. CIRCUMFERENCE 7th Grade Calculate with circumferences and areas of circles.

  2. The circumference of a circle is The distance around a circle Hint: Circumference remember circle around

  3. 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!

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

  5. We use Pi as the measurement to help us find the circumference of a circle. Pi, not Pie!

  6. HINT: Pi =3.14

  7. 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.

  8. 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.

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

  10. 3in C = 2 x 3.14 x r

  11. 8ft C = 3.14 d

  12. 122mm C = 2 x 3.14 x d

  13. 17.5 cm C = 3.14 x d

  14. 122.5mm C = 2 x 3.14 x r

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

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

  17. 8ft C = 3.14 d The answer is: 25.1ft

  18. 122mm C = 2 x 3.14 x d The answer is: 766.2mm

  19. 17.5 cm C = 3.14 x d The answer is: 55cm

  20. 122.5mm C = 2 x 3.14 x r The answer is: 76,930mm

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