Thực hiện các phép tính (tính hợp lí nếu có thể). (a) 2 /3 − − 3 /7 ;

a)\[\frac{2}{3} - \frac{{ - 3}}{7} = \frac{{14}}{{21}} - \frac{{ - 9}}{{21}} = \frac{{23}}{{21}}\];

b) \[\frac{2}{3} + \frac{4}{5}:\frac{{ - 3}}{5} = \frac{2}{3} + \frac{4}{5}.\frac{{ - 5}}{3} = \frac{2}{3} + \frac{{ - 4}}{3} = \frac{{ - 2}}{3}\];

c) \[3\frac{1}{2} + \frac{7}{3}:\frac{{ - 5}}{3} - 0,4 = \frac{7}{2} + \frac{7}{3}.\frac{{ - 3}}{5} - 0,4 = \frac{7}{2} + \frac{{ - 7}}{5} - 0,4\]

\[ = \frac{{35}}{{10}} + \frac{{ - 14}}{{10}} - \frac{4}{{10}} = \frac{{17}}{{10}}\];

d) \(9,125 + \left[ {0,25 - \left( {8,125 - 5,25} \right)} \right]\)

\( = 9,125 + 0,25 - 8,125 + 5,25\)

\( = \left( {9,125 - 8,125} \right) + \left( {0,25 + 5,25} \right)\)

\( = 1 + 5,5 = 6,5\).