Thực hiện phép tính (tính hợp lí nếu có thể):     a) 3/4- 0,25 + 1 1/2; b) 4/5 + 3/5.(-2/15)

a) \(\frac{3}{4} - 0,25 + 1\frac{1}{2}\)

\( = \frac{3}{4} - \frac{1}{4} + 1\frac{1}{2}\)

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

\( = \frac{1}{2} + 1\frac{1}{2}\)

\( = 2\).

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

\( = \frac{{ - 31}}{{15}}.\frac{{10}}{{31}} + \frac{3}{4}:\frac{3}{4}\)

\( =  - \frac{2}{3} + \frac{3}{4}.\frac{2}{3}\)

\( =  - \frac{2}{3} + \frac{1}{2}\)

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

b) \(\frac{4}{5} + \frac{3}{5}.\left( { - \frac{2}{{15}}} \right)\)

\( = \frac{4}{5} + \frac{{ - 2}}{{25}}\)

\( = \frac{{20}}{{25}} + \frac{{ - 2}}{{25}}\)

\( = \frac{{18}}{{25}}\);

d) \( - \frac{5}{7} \cdot \frac{2}{{11}} + \frac{{ - 5}}{7} \cdot \frac{9}{{11}} + \frac{{ - 5}}{7}\)

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

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

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

\( =  - \frac{5}{7} + \frac{{ - 5}}{7}\)

\( = \frac{{ - 10}}{7}\).