Решение:
\(\frac{5}{12} = \frac{5 \cdot 2}{12 \cdot 2} = \frac{10}{24}\)
\(\frac{3}{8} = \frac{3 \cdot 3}{8 \cdot 3} = \frac{9}{24}\)
\(\frac{10}{24} + \frac{9}{24} = \frac{19}{24}\)
\(\frac{19}{24} : \frac{12}{19} = \frac{19}{24} \cdot \frac{19}{12} = \frac{19 \cdot 19}{24 \cdot 12} = \frac{361}{288}\)
Ответ: 361/288.