Thực hiện phép tính (tính hợp lí nếu có thể): a) (1/4+ 2/5 - 3/2);b) 5/6- [- 4/5 - (1/3 +2/5)]

a) \(\frac{1}{4} + \frac{2}{5}\,\,.\,\,\frac{{ - 3}}{2}\)

\( = \frac{1}{4} + \frac{{ - 3}}{5}\)

\( = \frac{5}{{20}} - \frac{{12}}{{20}}\)

\( =  - \frac{7}{{20}}\);

b) \(\frac{5}{6} - \left[ {\frac{{ - 4}}{5} - \left( {\frac{1}{3} + \frac{2}{5}} \right)} \right]\)

\( = \frac{5}{6} - \frac{{ - 4}}{5} + \left( {\frac{1}{3} + \frac{2}{5}} \right)\)

\( = \frac{5}{6} + \frac{4}{5} + \frac{1}{3} + \frac{2}{5}\)

\( = \left( {\frac{5}{6} + \frac{1}{3}} \right) + \left( {\frac{4}{5} + \frac{2}{5}} \right)\)

\( = \frac{7}{6} + \frac{6}{5}\)

\( = \frac{{35}}{{30}} + \frac{{36}}{{30}} = \frac{{71}}{{30}}\).

c) \(3,2.\frac{{ - 11}}{{17}} + 3,2.\frac{{ - 6}}{{17}} + 4\)

\( = 3,2.\left( {\frac{{ - 11}}{{17}} + \frac{{ - 6}}{{17}}} \right) + 4\)

\( = 3,2.\left( { - 1} \right) + 4\)

\( =  - 3,2 + 4\)

\( = 0,8\).