18) \(\frac{1}{3}:0,4\)

\(0.4=\frac{2}{5}\). Тогда:

\(\frac{1}{3}:\frac{2}{5}=\frac{1}{3}\cdot\frac{5}{2}=\frac{5}{6}\).

Ответ: \(\frac{5}{6}\)