Finding Circumference for 4th and 5th Grade

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Finding Circumferencefor 4th and 5th Grade

• By Andrea Klee

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What Is Circumference

• Circumference is the distance all the way around
  a circle.
• The equation to find circumference is 2?r or ?
  multiplied by the diameter of the circle.

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Some Terms Defined

• ? is said as pie, like the kind you eat
• about 3.14
• r is the radius of a circle
• or half the distance across a circle
• d is the diameter of a circle
• or the distance all the way across a circle
• or two radii added together

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How To Find Circumference

• If you have the radius
• Multiply the radius by 2 to get the diameter.
• Multiply this answer by 3.14 (? ).
• If you have the diameter
• Multiply the diameter by 3.14 (?).

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Lets Try A Problem

• Find the diameter or the radius.
• We are going to find the radius.
• What is the radius of this circle?

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Problem Continued

• The radius is 5.
• Next, multiply the radius by 2 to get the
  diameter.
• Last, multiply the diameter by ? or 3.14.

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Problem Solved

• The circumference of the circle is 31.4.

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Heres Another Problem

• Find the circumference of this circle.

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Solution

• The diameter is 6.
• Multiply the diameter by ? (3.14).
• The Circumference is 18.84.

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Links

• Math.com has everything you might want to know
  about the parts of circles.
• This site defines circle, pie, circumference,
  diameter, and radius.
•  http//www.math.com/tables/geometry/circles.htm

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Links

• Prime Mathematics Enrichment is a magazine that
  has fun projects to do involving circles.
• http//www.nrich.maths.org.uk/prime/feb01/magazine
  .html

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Links

• Math Forums Ask Dr. Math
• This page is a letter sent to Dr. Math asking how
  the circumference of the Earth was first
  measured. This offers a little history about
  circumference.
• http//mathforum.org/library/drmath/view/58988.htm
  l