2. Найдите значение выражений. a) $$\frac{5}{11} - \frac{3}{11} + \frac{7}{11}$$ б) $$9\frac{13}{19} + (8\frac{18}{19} - 3\frac{15}{19})$$ в) $$18\frac{4}{21} - (10\frac{10}{21} + 3\frac{19}{21})$$

a) $$\frac{5}{11} - \frac{3}{11} + \frac{7}{11} = \frac{5-3+7}{11} = \frac{9}{11}$$. б) $$9\frac{13}{19} + (8\frac{18}{19} - 3\frac{15}{19}) = 9\frac{13}{19} + 5\frac{3}{19} = 14\frac{16}{19}$$. в) $$18\frac{4}{21} - (10\frac{10}{21} + 3\frac{19}{21}) = 18\frac{4}{21} - 13\frac{29}{21} = 18\frac{4}{21} - 14\frac{8}{21} = 3\frac{17}{21}$$. Ответ: a) $$\frac{9}{11}$$, б) $$14\frac{16}{19}$$, в) $$3\frac{17}{21}$$