Решение:
- а) \( \frac{6}{13} + \frac{8}{13} = \frac{6+8}{13} = \frac{14}{13} = 1\frac{1}{13} \)
- б) \( 4 - 1\frac{3}{5} = 4 - \frac{8}{5} = \frac{20}{5} - \frac{8}{5} = \frac{12}{5} = 2\frac{2}{5} \)
- в) \( \frac{2}{9} \cdot \frac{9}{10} = \frac{2 \cdot 9}{9 \cdot 10} = \frac{18}{90} = \frac{1}{5} \)
- г) \( \frac{2}{5} : 2 = \frac{2}{5} \cdot \frac{1}{2} = \frac{2 \cdot 1}{5 \cdot 2} = \frac{2}{10} = \frac{1}{5} \)
Ответ: а) $$1\frac{1}{13}$$, б) $$2\frac{2}{5}$$, в) $$\frac{1}{5}$$, г) $$\frac{1}{5}$$.