30. 3/5 : 1 2/3.

\(1\frac{2}{3}=\frac{5}{3}\).

\(\frac{3}{5}:\frac{5}{3}=\frac{3}{5}\cdot\frac{3}{5}=\frac{9}{25}\).

Ответ: \(\frac{9}{25}\).