Big Ideas Math: Modeling Real Life, Grade 7
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Big Ideas Math: Modeling Real Life, Grade 7 View details
1. Circles and Circumference
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Exercise 18 Page 367

Recall the formula for finding circumference of a circle given its radius.

19.43 inches

Practice makes perfect

Consider the shape of the sewer plate on a diagram.

We want to estimate the radius of this circle given the circumference. The circumference C of a circle with radius r is calculated using the formula below. C=2π r From the figure, we know that the circumference of the circle is 122 inches. We can substitute 122 for C in the formula and then calculate r. We will use 3.14 as an estimate for π.
C=2π r
122=2( 3.14)(r)
122=6.28r
122/6.28=r
r=122/6.28
r=19.426751 ...
r≈ 19.43
The radius of the circle is approximately 19.43 inches.

Extra

More About Circles!

Are you interested in learning more about circles? Our Mathleaks original content can teach you all about them! Check out the following resources to see real-world uses for circumference and area, how circles compare to other shapes and why, as well as some higher level topics that you can look forward to learning about in Geometry and Algebra 2.