Решение:
\[ \frac{3}{18} + \frac{5}{27} = \frac{3 \times 3}{18 \times 3} + \frac{5 \times 2}{27 \times 2} = \frac{9}{54} + \frac{10}{54} \]
\[ \frac{9}{54} + \frac{10}{54} = \frac{9 + 10}{54} = \frac{19}{54} \]
Ответ: $$\frac{19}{54}$$