15) 2 2/3 : 2 6/7

\(2\frac{2}{3}=\frac{8}{3}\), \(2\frac{6}{7}=\frac{20}{7}\).

\(\frac{8}{3}:\frac{20}{7}=\frac{8}{3}\cdot\frac{7}{20}=\frac{14}{15}\).

Ответ: \(\frac{14}{15}\).