Thực hiện phép tính (hợp lý nếu được): (a) 1/4 + − 5/12 − -7/6 . (b) − 34 , 67 + 21 , 88 .

a) \(\frac{1}{4} + \frac{{ - 5}}{{12}} - \frac{{ - 7}}{6}\)

\( = \frac{3}{{12}} + \frac{{ - 5}}{{12}} - \frac{{ - 14}}{{12}}\)

\( = \frac{{ - 2}}{{12}} - \frac{{ - 14}}{{12}}\)

\( = \frac{{12}}{{12}} = 1\).

b) \( - 34,67 + 21,88\)

\( = - 12,79\).

c) \(\frac{{14}}{3} \cdot \frac{{ - 4}}{9} - \frac{{14}}{3} \cdot \frac{5}{9} + \frac{{11}}{3}\)

\( = \frac{{14}}{3} \cdot \left( {\frac{{ - 4}}{9} - \frac{5}{9}} \right) + \frac{{11}}{3}\)

\( = \frac{{14}}{3} \cdot \left( { - 1} \right) + \frac{{11}}{3} = \frac{{ - 14}}{3} + \frac{{11}}{3} = - 1\).

d) \(\frac{{ - 8}}{9} + \frac{{15}}{7} + 2\frac{1}{4} + \frac{6}{7} + \frac{{ - 10}}{9}\)

\( = \left( {\frac{{ - 8}}{9} + \frac{{ - 10}}{9}} \right) + \left( {\frac{{15}}{7} + \frac{6}{7}} \right) + 2\frac{1}{4}\)

\( = \left( { - 2} \right) + 3 + \frac{9}{4} = 1 + \frac{9}{4} = \frac{{13}}{4}\).