Thực hiện phép tính (tính hợp lí nếu có thể):     a)1/8 - 9/8.4/3;  b) 2/11.- 5/4 +- 9/11.5/4+ 1 3/4

a) \(\frac{1}{8} - \frac{9}{8}.\frac{4}{3}\)

\( = \frac{1}{8} - \frac{3}{2}\)

\( = \frac{1}{8} - \frac{{12}}{8}\)

\( = \frac{{ - 11}}{8}\).

b) \(\frac{2}{{11}}.\frac{{ - 5}}{4} + \frac{{ - 9}}{{11}}.\frac{5}{4} + 1\frac{3}{4}\)

\( = \frac{2}{{11}}.\frac{{ - 5}}{4} + \frac{9}{{11}}.\frac{{ - 5}}{4} + \frac{7}{4}\)

\( = \frac{{ - 5}}{4}.\left( {\frac{2}{{11}} + \frac{9}{{11}}} \right) + \frac{7}{4}\)

\( = \frac{{ - 5}}{4}.1 + \frac{7}{4}\)

\[ = \frac{5}{4} + \frac{7}{4}\]

\[ = \frac{{12}}{4} = 3\].

c) \(\left( { - 2,4 + \frac{1}{3}} \right):3,1 + 75\% :1\frac{1}{2}\)

\[ = \left( { - \frac{{24}}{{10}} + \frac{1}{3}} \right):\frac{{31}}{{10}} + \frac{{75}}{{100}}:\frac{3}{2}\]

\[ = \left( { - \frac{{12}}{5} + \frac{1}{3}} \right).\frac{{10}}{{31}} + \frac{3}{4}.\frac{2}{3}\]

\[ = \frac{{ - 31}}{{15}}.\frac{{10}}{{31}} + \frac{1}{2}\]

\[ = \frac{{ - 2}}{3} + \frac{1}{2}\]

\[ = \frac{{ - 4}}{6} + \frac{3}{6} =  - \frac{1}{6}\].