Math CentralQuandaries & Queries


Question from Tracey:

I own a custom workroom, I am figuring out fabric quantities or an estimate. When
at the job site, I forgot to measure the diameter of the semi circle shape that I have to
make a cushion for!!!
If the circumference of the semi circle is 165" what would the diameter be, maybe half
this measurement????

I appreciate any help...I basically need the width from left to right to see if I can fit
the cushion on one width of fabric that is 52" wide!

Hi Tracey,

The relationship between the circumference $C$ and the diameter $D$ of a circle is

\[C = \pi \; D\]

where $\pi$ is approximately 3.1516. Thus if you know the diameter of a circle you can find the circumference by multiplying the diameter by $ \pi.$

If you divide both sides of the equation above by $\pi$ it becomes

\[D = \frac{C}{\pi}\]

and hence if you know the circumference of a circle you can find its diameter by dividing the circumference by $\pi.$

I hope this helps,

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