\[\boxed{\text{17\ (17).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[1)\ \frac{5}{15} = \frac{5\ :5}{15\ :5} = \frac{1}{3}\]
\[2)\ \frac{12}{18} = \frac{12\ :6}{18\ :6} = \frac{2}{3}\]
\[3)\ \frac{27}{45} = \frac{27\ :9}{45\ :9} = \frac{3}{5}\]
\[4)\ \frac{30}{48} = \frac{30\ :6}{48\ :6} = \frac{5}{8}\ \]