If $\mathrm{a}, \mathrm{b}, \mathrm{c}, \mathrm{d}$ are four distinct numbers chosen from the set $\{1,2,3 \ldots, 9\}$, then the minimum value of $\frac{\mathrm{a}}{\mathrm{b}}+\frac{\mathrm{c}}{\mathrm{d}}$ is