Thực hiện phép tính (tính hợp lí nếu có thể): a) 15/47 + (-8/33) +32/47 + (-25/33)                 b) 1/4 . căn 64 - căn 9/4

a) \[\frac{{15}}{{47}} + \frac{{ - 8}}{{33}} + \frac{{32}}{{47}} + \frac{{ - 25}}{{33}} = \left( {\frac{{15}}{{47}} + \frac{{32}}{{47}}} \right) + \left( {\frac{{ - 8}}{{33}} + \frac{{ - 25}}{{33}}} \right) = 0\].b) \[\frac{1}{4}.\sqrt {64} - \sqrt {\frac{9}{4}} = \frac{1}{4}.8 - \frac{3}{2} = \frac{1}{2}\].c) \[\frac{5}{9} \cdot \frac{7}{{11}} + \frac{5}{9} \cdot \frac{{19}}{{11}} - \frac{5}{9}.\frac{8}{{11}} = \frac{5}{9}\left( {\frac{7}{{11}} + \frac{{19}}{{11}} - \frac{8}{{11}}} \right) = \frac{5}{9}.\frac{{18}}{{11}} = \frac{{10}}{{11}}\].d)\[\left| {\frac{{ - 1}}{3}} \right| + \frac{2}{3}.\left( {\frac{{ - 2}}{5}} \right) = \frac{1}{3} + \frac{{ - 4}}{{15}} = \frac{5}{{15}} + \frac{{ - 4}}{{15}} = \frac{1}{{15}}\].