What is the circumference of a circle with a radius = 4.25 in? What is the circumference of a circle with a diameter = 27.8 m?

1 Answer
Mar 1, 2018

The first circumference is 26.69 and the second is 87.292

Explanation:

The formula for finding the circumference of a circle is 2pir2πr
Think about it this way: Multiply 2 xx× radius of the circle xx× piπ (which is always going to be 3.143.14).
The first question tells you the radius, so we already know that r = 4.25r=4.25 All we have to do now is plug that into our equation.

(2 xx 3.14) xx 4.25(2×3.14)×4.25 (now multiply 22 and 3.143.14 together)
6.28 xx 4.25 = 26.696.28×4.25=26.69 (now multiply 6.286.28 and 4.254.25 together)
There's your first answer!

The second one is a little more complicated, but still fairly straightforward. The radius of a circle is always half of the diameter , so divide 27.8/2 = 13.927.82=13.9. Now we know r = 13.9r=13.9. Let's plug that in.
(2 xx 3.14) xx 13.9(2×3.14)×13.9 (now multiply 22 and 3.143.14 together)
6.28 xx 13.9 = 87.2926.28×13.9=87.292 (now multiply 6.286.28 and 13.913.9 together)
There's your second answer!