To find the sum of the fractions \( \frac{12}{31} + \frac{13}{31} \), you can add the numerators since the denominators are the same.
\[ \frac{12}{31} + \frac{13}{31} = \frac{12 + 13}{31} = \frac{25}{31} \]
Thus, the sum of the fractions is \( \frac{25}{31} \).