Thực hiện phép tính (tính hợp lí nếu có thể):  a) 4/5 +3/5.(-2/15);b) - 3/4.2022/2023 - 2022/2023.1/4

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

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

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

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

b) \[\frac{{ - 3}}{4}.\frac{{2022}}{{2023}} - \frac{{2022}}{{2023}}.\frac{1}{4}\]

\( = \frac{{2022}}{{2023}}.\left( {\frac{{ - 3}}{4} - \frac{1}{4}} \right)\)

\( = \frac{{2022}}{{2023}}.\left( { - 1} \right)\)

\( =  - \frac{{2022}}{{2023}}\).

c) \[\frac{{ - 1}}{4}.\left( {12\frac{3}{4} - 7,75} \right) - 25\% .3\frac{1}{2}\]

\[ = \frac{{ - 1}}{4}.\left( {12,75 - 7,75} \right) - \frac{{25}}{{100}}.\frac{7}{2}\]

\[ = \frac{{ - 1}}{4}.5 - \frac{1}{4}.\frac{7}{2}\]

\[ = \frac{{ - 5}}{4} - \frac{7}{8}\]

\[ = \frac{{ - 10}}{8} - \frac{7}{8}\]

\[ = \frac{{ - 17}}{8}\].