3. Выполните действия: a) $$(9 - 2\frac{3}{11}) + (2 + 1\frac{9}{11})$$; б) $$28\frac{2}{21} - (14\frac{17}{21} + 11\frac{8}{21})$$

3. Выполнение действий:

1. a) \((9 - 2\frac{3}{11}) + (2 + 1\frac{9}{11}) = (8 \frac{11}{11} - 2 \frac{3}{11}) + (3 \frac{9}{11}) = 6 \frac{8}{11} + 3 \frac{9}{11} = (6 + 3) + (\frac{8}{11} + \frac{9}{11}) = 9 + \frac{17}{11} = 9 + 1 \frac{6}{11} = 10 \frac{6}{11}\)

2. б) \(28\frac{2}{21} - (14\frac{17}{21} + 11\frac{8}{21}) = 28\frac{2}{21} - ( (14 + 11) + (\frac{17}{21} + \frac{8}{21}) ) = 28\frac{2}{21} - (25 + \frac{25}{21}) = 28\frac{2}{21} - (25 + 1 \frac{4}{21}) = 28\frac{2}{21} - 26 \frac{4}{21} = 27 \frac{23}{21} - 26 \frac{4}{21} = (27 - 26) + (\frac{23}{21} - \frac{4}{21}) = 1 + \frac{19}{21} = 1 \frac{19}{21}\)

Ответ: a) \(10 \frac{6}{11}\); б) \(1 \frac{19}{21}\).