# 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?

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 $2 \pi r$
Think about it this way: Multiply 2 $\times$ radius of the circle $\times$ $\pi$ (which is always going to be $3.14$).
The first question tells you the radius, so we already know that $r = 4.25$ All we have to do now is plug that into our equation.

$\left(2 \times 3.14\right) \times 4.25$ (now multiply $2$ and $3.14$ together)
$6.28 \times 4.25 = 26.69$ (now multiply $6.28$ and $4.25$ together)
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 $\frac{27.8}{2} = 13.9$. Now we know $r = 13.9$. Let's plug that in.
$\left(2 \times 3.14\right) \times 13.9$ (now multiply $2$ and $3.14$ together)
$6.28 \times 13.9 = 87.292$ (now multiply $6.28$ and $13.9$ together)