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# help with proportion

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The circumference of a circle varies directly as the diameter of a circle. When the diameter of a circle is 5, the circumference of the circle is approximately 15.7.What is the approximate circumference of a circle with a diameter of 9? Round answer to nearest tenth.

Mar 4, 2021

### 1+0 Answers

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We don't need to do proportions

C = pi*d

3.14*9=28.26≈28.3

However, if you do want to solve this problem with proportions, you can do the following:

We can get the proportion by making a fraction with 9 (diameter of 2nd circle) on the top and 5 (diameter of first circle) on the bottom, $$\frac{9}{5}$$

If the circumference of the circle with the diameter of 5 is 15.7, we can multiply 15.7 by $$\frac{9}{5}$$ and get 28.26, which rounds to 28.3

Mar 4, 2021
edited by swag123456  Mar 4, 2021