Выполни действия: a) $$rac{12}{13} - \frac{5}{13} + \frac{4}{13}$$; б) $$5\frac{7}{11} + 1\frac{9}{11}$$; в) $$7 - 3\frac{5}{9}$$; г) $$6\frac{5}{11} - 4\frac{9}{11}$$

a) $$\frac{12}{13} - \frac{5}{13} + \frac{4}{13} = \frac{12-5+4}{13} = \frac{11}{13}$$

б) $$5\frac{7}{11} + 1\frac{9}{11} = (5+1) + (\frac{7}{11} + \frac{9}{11}) = 6 + \frac{16}{11} = 6 + 1\frac{5}{11} = 7\frac{5}{11}$$

в) $$7 - 3\frac{5}{9} = 6\frac{9}{9} - 3\frac{5}{9} = (6-3) + (\frac{9}{9} - \frac{5}{9}) = 3 + \frac{4}{9} = 3\frac{4}{9}$$

г) $$6\frac{5}{11} - 4\frac{9}{11} = 5\frac{16}{11} - 4\frac{9}{11} = (5-4) + (\frac{16}{11} - \frac{9}{11}) = 1 + \frac{7}{11} = 1\frac{7}{11}$$