Data and Displays · Hard problem

Thirty-one values are grouped into bins $0$–$9$: $4$, $\ 10$–$19$: $9$, $\ 20$–$29$: $x$, $\ 30$–$39$: $y$, $\ 40$–$49$: $3$, with $x + y = 15$. The median lies in the $20$–$29$ bin. What is the smallest possible value of $x$?