П.85 Вычислите: a) $$10\frac{8}{13} + 6\frac{5}{13} - 3\frac{9}{13}$$; б) $$14\frac{27}{45} - 3\frac{8}{45} + 5\frac{6}{45}$$; в) $$8\frac{6}{20} - (5 - 2\frac{3}{20})$$; г) $$10\frac{22}{23} - (5\frac{4}{23} - 4\frac{5}{23})$$.

а)

$$10\frac{8}{13} + 6\frac{5}{13} - 3\frac{9}{13} = (10+6-3) + (\frac{8}{13} + \frac{5}{13} - \frac{9}{13}) = 13 + \frac{4}{13} = 13\frac{4}{13}$$

б)

$$14\frac{27}{45} - 3\frac{8}{45} + 5\frac{6}{45} = (14 - 3 + 5) + (\frac{27}{45} - \frac{8}{45} + \frac{6}{45}) = 16 + \frac{25}{45} = 16\frac{5}{9}$$

в)

$$8\frac{6}{20} - (5 - 2\frac{3}{20}) = 8\frac{6}{20} - 5 + 2\frac{3}{20} = (8 - 5 + 2) + (\frac{6}{20} + \frac{3}{20}) = 5 + \frac{9}{20} = 5\frac{9}{20}$$

г)

$$10\frac{22}{23} - (5\frac{4}{23} - 4\frac{5}{23}) = 10\frac{22}{23} - 5\frac{4}{23} + 4\frac{5}{23} = (10 - 5 + 4) + (\frac{22}{23} - \frac{4}{23} + \frac{5}{23}) = 9 + \frac{23}{23} = 9 + 1 = 10$$

Ответ: а) $$13\frac{4}{13}$$; б) $$16\frac{5}{9}$$; в) $$5\frac{9}{20}$$; г) 10.