Do not add the denominators. Find a common denominator, rewrite each fraction, and add the numerators.

$\displaystyle\frac{{5}}{{8}}+\frac{{7}}{{12}}=\frac{{15}}{{24}}+\frac{{14}}{{24}}=\frac{{29}}{{24}}={1}\frac{{5}}{{24}}\usepackage{cmbright}\Huge\$

The correct answer is $\displaystyle{1}\frac{{5}}{{24}}\usepackage{cmbright}\Huge\$ .