Thực hiện các phép tính sau (a) 7/12 − 5/6 + − 3/8 .

a) \[\frac{7}{{12}} - \frac{5}{6} + \frac{{ - 3}}{8} = \frac{{14}}{{24}} - \frac{{20}}{{24}} + \frac{{ - 9}}{{24}} = \frac{{ - 5}}{8}\].

b) \[\frac{2}{9} + \frac{7}{9}:\left( {\frac{1}{3} - \frac{{ - 1}}{4}} \right) = \frac{2}{9} + \frac{7}{9}:\frac{7}{{12}} = \frac{2}{9} + \frac{{12}}{9} = \frac{{14}}{9}\].