Question

What is the approximate area of a circle with a radius of 10 in?

Answer 1

`\huge\boxed{\textsf{A.}\ 78.5\ \text{in}^2}`

Correction to your question text: diameter, not radius.

The area of a circle is given by:

`A=\pi r^2`

The radius is half of the diameter.

`A=\pi\cdot\left((10)/(2)\right)^2`

Substitute and solve.

`\begin{aligned}A&=\pi\cdot\left((10)/(2)\right)^2\\&=\pi\cdot5^2\\&=\pi\cdot25\\&\approx\boxed{78.5}\end{aligned}`