IMAS 2025-2026 Junior Division - First Round Question 11

Question 11

As shown in the diagram below, $ABC$ is a triangle where $AB=AC$ and the angle bisector of $\angle ABC$ intersects $AC$ at $D$. If $BC=BD+AD$, what is the measure, in degrees, of $\angle CBD$?

Question illustration

$15^\circ$
$20^\circ$
$24^\circ$
$30^\circ$
$40^\circ$