Let's start by assigning a "nice" value to the radius of the smallest circle.
Let's say the blue circle has radius 1

If the blue circle has radius 1, then the DIAMETER of the blue circle must be 2.

This means the radius of the green circle must be 2

If the radius of the green circle is 2, then the DIAMETER of the green circle must be 4.

This means the radius of the red circle must be 4


Area of circle \(= \pi r^2\)
So, the area of the red circle \(= \pi (4^2) = 16\pi\)

And the area of ONE blue circle \(= \pi (1^2) = \pi\)
So, the area of TWO blue circles \(= 2\pi\)

What fraction of the largest circular region is shaded?
Answer \(= \frac{2\pi}{16\pi} = \frac{1}{8}\)

Answer: B