# Math Help - circle

1. ## circle

A coin is unique in that the outer edge is gold while the inside is silver. Assuming both sides of the coin are identical, and a line tangent to the inner circle is 23 mm from edge to edge of the coin, and excluding the edge of the coin in the calculation, what is the surface area of gold on the coin, in square millimetres? Please round up to the nearest square millimetre.

I am really not good at this, can someone point me in the right direction please?

2. If $R$ is the radius of the coin and $r$ is the radius of the silver circle, the gold area is $\pi R^2-\pi r^2=\pi (R^2-r^2)$.
We have $R^2-r^2=\left(\frac{23}{2}\right)^2$.

3. Thank you!