2022 SSMO Accuracy Round Problems/Problem 8

Problem

Let $ABCD$ be a trapezoid with $AB \parallel CD$. Suppose that $AD=1$, $DC=4$, $CB=2$, and $AB<CD$. Let $X$ be the midpoint of $AB$. If $E$ is the intersection of $AC$ and $BD$, and $\angle XEB=\angle ADC$, then $AB=\frac{m}{n}$, where $m$ and $n$ are relatively prime positive integers. Find $m+n.$

Solution