**Решение:**
a) $$\frac{5}{8} : 2\frac{11}{14} = \frac{5}{8} : \frac{2 \cdot 14 + 11}{14} = \frac{5}{8} : \frac{39}{14} = \frac{5}{8} \cdot \frac{14}{39} = \frac{5 \cdot 14}{8 \cdot 39} = \frac{5 \cdot 2 \cdot 7}{2 \cdot 4 \cdot 39} = \frac{5 \cdot 7}{4 \cdot 39} = \frac{35}{156}$$.
**Ответ:** $$\frac{35}{156}$$