Решение:

1) a)

$$\frac{0,4 \cdot \frac{1}{3}}{\frac{5}{6} \cdot 1,2} = \frac{\frac{0,4}{3}}{\frac{5 \cdot 1,2}{6}} = \frac{\frac{0,4}{3}}{\frac{6}{6}} = \frac{0,4}{3} = \frac{4}{30} = \frac{2}{15}$$

б)

$$\frac{2,5 \cdot \frac{4}{5}}{1,6 \cdot \frac{3}{4}} = \frac{\frac{2,5 \cdot 4}{5}}{\frac{1,6 \cdot 3}{4}} = \frac{\frac{10}{5}}{\frac{4,8}{4}} = \frac{2}{1,2} = \frac{20}{12} = \frac{5}{3} = 1\frac{2}{3}$$

2) a)

$$\frac{0,4 + \frac{1}{3}}{\frac{5}{6} + 1,2} = \frac{\frac{4}{10} + \frac{1}{3}}{\frac{5}{6} + \frac{12}{10}} = \frac{\frac{12 + 10}{30}}{\frac{25+36}{30}} = \frac{\frac{22}{30}}{\frac{61}{30}} = \frac{22}{61}$$

б)

$$\frac{2,5 - \frac{4}{5}}{1,6 - \frac{3}{4}} = \frac{\frac{25}{10} - \frac{4}{5}}{\frac{16}{10} - \frac{3}{4}} = \frac{\frac{5}{2} - \frac{4}{5}}{\frac{8}{5} - \frac{3}{4}} = \frac{\frac{25 - 8}{10}}{\frac{32 - 15}{20}} = \frac{\frac{17}{10}}{\frac{17}{20}} = \frac{17 \cdot 20}{10 \cdot 17} = \frac{2}{1} = 2$$