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.

$A=\pi\cdot\left(\dfrac{10}{2}\right)^2$

Substitute and solve.

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