13) 1 3/4 * 4/5

13) $$ 1\frac{3}{4} \cdot \frac{4}{5} = \frac{1 \cdot 4 + 3}{4} \cdot \frac{4}{5} = \frac{7}{4} \cdot \frac{4}{5} = \frac{7 \cdot 4}{4 \cdot 5} = \frac{7}{5} = 1\frac{2}{5} $$

Ответ: $$1\frac{2}{5}$$