# Thread: Find the ratio of the white to the shaded area..?

1. ## Find the ratio of the white to the shaded area..?

Ok well...
The diagram shows 2 concentric circles. The large one has a radius of 5cm and the smaller one has a radius of 3cm.

Find the ratio of the white to the shaded area..?

Ok well...
The diagram shows 2 concentric circles. The large one has a radius of 5cm and the smaller one has a radius of 3cm.

Find the ratio of the white to the shaded area..?

The area of the shaded area is $9 \pi$ using $A=\pi r^2$

The area of the bigger circle is $25 \pi$ using the same reasoning.

The difference between these areas is the area of the white part which would be $25 \pi - 9 \pi = 16 \pi$

The ratio of the white to the shaded area would then be:

$\frac{16 \pi}{9 \pi}=\frac{16}{9}$