a) $$ \frac{6}{17} \cdot \frac{8}{19} \cdot 1 \frac{5}{8} = \frac{6}{17} \cdot \frac{8}{19} \cdot \frac{13}{8} = \frac{6 \cdot 8 \cdot 13}{17 \cdot 19 \cdot 8} = \frac{624}{2584} = \frac{78}{323} $$
Ответ: $$\frac{78}{323}$$