Thực hiện phép tính (tính hợp lí nếu có thể): a) 2/3 - (- 5/7 + 2/3)

a) \(\frac{2}{3} - \left( {\frac{{ - 5}}{7} + \frac{2}{3}} \right)\)\( = \frac{2}{3} + \frac{5}{7} - \frac{2}{3}\)

\( = \left( {\frac{2}{3} - \frac{2}{3}} \right) + \frac{5}{7}\)\( = 0 + \frac{5}{7}\)\( = \frac{5}{7}.\)

b) \[60,7 + 25,5--38,7\]

\[ = \left( {60,7--38,7} \right) + 25,5\]

\[ = 22 + 25,5\]

\( = 47,5.\)

c) \(\frac{2}{3}:\left( {\frac{2}{5} + \frac{1}{2}} \right) + \frac{2}{3}:\left( {\frac{1}{4} - \frac{4}{7}} \right)\)

\( = \frac{2}{3}:\frac{9}{{10}} + \frac{2}{3}:\frac{{ - 9}}{{28}}\)

\( = \frac{2}{3} \cdot \frac{{10}}{9} + \frac{2}{3} \cdot \frac{{ - 28}}{9}\)

\[ = \frac{2}{3} \cdot \left( {\frac{{10}}{9} + \frac{{ - 28}}{9}} \right)\]

\( = \frac{2}{3} \cdot \left( { - 2} \right) = \frac{{ - 4}}{3}\).

d) \[{\left( { - 2} \right)^3} \cdot \frac{{ - 1}}{{24}} + \left( {80\%  - 1,2} \right):\frac{2}{{15}}\]

\( = \left( { - 8} \right) \cdot \frac{{ - 1}}{{24}} + \left( {\frac{4}{5} - \frac{6}{5}} \right) \cdot \frac{{15}}{2}\)

\( = \frac{1}{3} + \frac{{ - 2}}{5} \cdot \frac{{15}}{2}\)

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

\( = \frac{1}{3} + \frac{{ - 9}}{3} = \frac{{ - 8}}{3}.\)