39. \(\frac{10}{20}-\frac{6}{18}\)

Сократим дроби: \(\frac{10}{20}=\frac{1}{2}\), \(\frac{6}{18}=\frac{1}{3}\).

\(\frac{1}{2}-\frac{1}{3}=\frac{3}{6}-\frac{2}{6}=\frac{1}{6}\).

Ответ: \(\frac{1}{6}\).