Вычислите: a) $$\frac{5}{11} + \frac{8}{11}$$; б) $$\frac{5}{7} - \frac{2}{7}$$; в) $$\frac{9}{13} + \frac{5}{13}$$; г) $$3 + (\frac{-9}{14})$$; д) $$-\frac{5}{9} - \frac{1}{12}$$; ж) $$-3 \frac{5}{9} : \frac{8}{21} : (\frac{-4}{7})$$

$$\bold{a)}$$ $$\frac{5}{11} + \frac{8}{11} = \frac{5+8}{11} = \frac{13}{11} = 1 \frac{2}{11}$$ $$\bold{Ответ: 1 \frac{2}{11}}$$ $$\bold{б)}$$ $$\frac{5}{7} - \frac{2}{7} = \frac{5-2}{7} = \frac{3}{7}$$ $$\bold{Ответ: \frac{3}{7}}$$ $$\bold{в)}$$ $$\frac{9}{13} + \frac{5}{13} = \frac{9+5}{13} = \frac{14}{13} = 1 \frac{1}{13}$$ $$\bold{Ответ: 1 \frac{1}{13}}$$ $$\bold{г)}$$ $$3 + (\frac{-9}{14}) = 3 - \frac{9}{14} = \frac{3 \cdot 14}{14} - \frac{9}{14} = \frac{42}{14} - \frac{9}{14} = \frac{42-9}{14} = \frac{33}{14} = 2 \frac{5}{14}$$ $$\bold{Ответ: 2 \frac{5}{14}}$$ $$\bold{д)}$$ $$-\frac{5}{9} - \frac{1}{12} = -(\frac{5}{9} + \frac{1}{12}) = -(\frac{5 \cdot 4}{9 \cdot 4} + \frac{1 \cdot 3}{12 \cdot 3}) = -(\frac{20}{36} + \frac{3}{36}) = -\frac{23}{36}$$ $$\bold{Ответ: -\frac{23}{36}}$$ $$\bold{ж)}$$ $$-3 \frac{5}{9} : \frac{8}{21} : (\frac{-4}{7}) = -\frac{32}{9} : \frac{8}{21} : (\frac{-4}{7}) = -\frac{32}{9} \cdot \frac{21}{8} \cdot (-\frac{7}{4}) = \frac{32 \cdot 21 \cdot 7}{9 \cdot 8 \cdot 4} = \frac{4 \cdot 3 \cdot 7}{9 \cdot 1 \cdot 4} = \frac{28}{3} = 9 \frac{1}{3}$$ $$\bold{Ответ: 9 \frac{1}{3}}$$