5. Let $x \neq y$, and the sequences $x, a_{1}, a_{2}, a_{3}, y$ and $b_{1}, x, b_{2}, b_{3}, y, b_{4}$ are both arithmetic sequences, $\frac{b_{4}-b_{3}}{a_{2}-a_{1}}=$ $\qquad$ .
5. $\frac{8}{3}$. $a_{2}-a_{1}=\frac{1}{4}(y-x), b_{4}-b_{3}=\frac{2}{3}(y-x)$, so $\frac{b_{4}-b_{3}}{a_{2}-a_{1}}=\frac{8}{3}$.