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$$\frac{W}{X}+\frac{Y}{Z}=\frac{WZ+XY}{XZ}$$ Small fractions have small numerators and large denominators. To maximize the denominator, let $X=8$ and $Z=9$. $$\frac{9W+8Y}{72}$$ To minimize the numerator, let $W=1$ and $Y=2$. $$\frac{9+16}{72}=\boxed{\frac{25}{72}}$$