4. Вычислить a) 3/4 + 1/8 б) 4 5/9 - 2 5/18 в) 1 3/5 * 5/8 г) 2 4/5 : 1 2/5

1. a) $$\frac{3}{4} + \frac{1}{8} = \frac{3 \cdot 2}{4 \cdot 2} + \frac{1}{8} = \frac{6}{8} + \frac{1}{8} = \frac{6 + 1}{8} = \frac{7}{8}$$
2. б) $$4\frac{5}{9} - 2\frac{5}{18} = 4\frac{5 \cdot 2}{9 \cdot 2} - 2\frac{5}{18} = 4\frac{10}{18} - 2\frac{5}{18} = (4 - 2) + (\frac{10}{18} - \frac{5}{18}) = 2\frac{10 - 5}{18} = 2\frac{5}{18}$$
3. в) $$1\frac{3}{5} \cdot \frac{5}{8} = \frac{1 \cdot 5 + 3}{5} \cdot \frac{5}{8} = \frac{8}{5} \cdot \frac{5}{8} = \frac{8 \cdot 5}{5 \cdot 8} = 1$$
4. г) $$2\frac{4}{5} : 1\frac{2}{5} = \frac{2 \cdot 5 + 4}{5} : \frac{1 \cdot 5 + 2}{5} = \frac{14}{5} : \frac{7}{5} = \frac{14}{5} \cdot \frac{5}{7} = \frac{14 \cdot 5}{5 \cdot 7} = \frac{14}{7} = 2$$

Ответ: а) $$\frac{7}{8}$$, б) $$2\frac{5}{18}$$, в) $$1$$, г) $$2$$