Thực hiện phép tính (tính hợp lí nếu có thể): a) 1,25.6.(- 8); b) 1/8- 9/8.4/3

a) \(1,25.6.\left( { - 8} \right)\)

\( = \left[ {1,25.\left( { - 8} \right)} \right].6\)

\( = \left( { - 10} \right).6\)

\( =  - 60\).

c) \(1\frac{{13}}{{15}}.0,75 - \left( {\frac{{11}}{{20}} + 25\% } \right):\frac{5}{7}\)

\( = \frac{{28}}{{15}}.\frac{3}{4} - \left( {\frac{{11}}{{20}} + \frac{1}{4}} \right).\frac{7}{5}\)

\( = \frac{7}{5} - \left( {\frac{{11}}{{20}} + \frac{5}{{20}}} \right).\frac{7}{5}\)

\( = \frac{7}{5} - \frac{{16}}{{20}}.\frac{7}{5}\)

\( = \frac{7}{5}.\left( {1 - \frac{{16}}{{20}}} \right)\)

\( = \frac{7}{5}.\frac{4}{{20}} = \frac{7}{{25}}\).

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

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

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

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

d) \(\frac{{ - 5}}{{17}}.\frac{{31}}{{33}} - \frac{5}{{17}}.\frac{2}{{33}} + 1\frac{5}{{17}}\)

\( = \frac{{ - 5}}{{17}}.\left( {\frac{{31}}{{33}} + \frac{2}{{33}}} \right) + \frac{{22}}{{17}}\)

\( = \frac{{ - 5}}{{17}}.1 + \frac{{22}}{{17}}\)

\( = \frac{{17}}{{17}} = 1\).