IKMC 2017 - Grades 11-12 - Self-study Question 6

Question 6

The diagram shows a circle with centre $O$ and diameters $AB$ and $CX$. Let $OB=BC$. What fraction of the circle area is shaded?

Question illustration

$\frac25$
$\frac13$
$\frac27$
$\frac38$
$\frac4{11}$