5) (-1 ⁷/₉)⁵ ⋅ (-1 ⁷/₉)¹² : (-1 ⁷/₉)²⁰ ;

5) $$ (-1 \frac{7}{9})^5 \cdot (-1 \frac{7}{9})^{12} : (-1 \frac{7}{9})^{20} = (-1 \frac{7}{9})^{5+12-20} = (-1 \frac{7}{9})^{-3} $$

$$(-1 \frac{7}{9})^{-3} = ( -\frac{16}{9})^{-3} = (-\frac{9}{16})^3 = -\frac{729}{4096}$$

Ответ: -729/4096