Thực hiện các phép tính sau một cách hợp lí. a) \(\frac{5}{{11}}.\frac{5}{7} + \frac{5}{{11}}.\frac{2}{7} + \frac{6}{{11}} - 2.\)          b) \(\left( {\frac{2}{7} + \frac{{ - 1}}{4}} \righ

a) \(\frac{5}{{11}}.\frac{5}{7} + \frac{5}{{11}}.\frac{2}{7} + \frac{6}{{11}} - 2.\)

\( = \frac{5}{{11}}.\left( {\frac{5}{7} + \frac{2}{7}} \right) + \frac{6}{{11}} - 2\)

\( = \frac{5}{{11}}.1 + \frac{6}{{11}} - 2\)

\( = \frac{5}{{11}} + \frac{6}{{11}} - 2\)

\( = 1 - 2 = - 1.\)

b) \(\left( {\frac{2}{7} + \frac{{ - 1}}{4}} \right) - \left( {\frac{{ - 5}}{7} - \frac{1}{4} + \frac{6}{{11}}} \right)\)

\( = \left( {\frac{2}{7} + \frac{{ - 1}}{4}} \right) - \left( {\frac{{ - 5}}{7} - \frac{1}{4} + \frac{6}{{11}}} \right)\)

\( = \frac{2}{7} + \frac{{ - 1}}{4} + \frac{5}{7} + \frac{1}{4} - \frac{6}{{11}}\)

\( = \left( {\frac{2}{7} + \frac{5}{7}} \right) + \left( {\frac{{ - 1}}{4} + \frac{1}{4}} \right) - \frac{6}{{11}}\)

\( = 1 + 0 - \frac{6}{{11}}\)

\( = 1 - \frac{6}{{11}} = \frac{5}{{11}}.\)