Thực hiện phép tính (tính hợp lí nếu có thể): a) \(\frac{2}{3} - \left( {\frac{{ - 5}}{7} + \frac{2}{3}} \right).\)   b) \[60,7 + 25,5--38,7.\] c) \[19\frac{5}{8}:\frac{7}{{12}} - 15\frac{

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) \[19\frac{5}{8}:\frac{7}{{12}} - 15\frac{1}{4}:\frac{7}{{12}}\]

\[ = \frac{{157}}{8} \cdot \frac{{12}}{7} - \frac{{61}}{4} \cdot \frac{{12}}{7}\]

\[ = \left( {\frac{{157}}{8} - \frac{{61}}{4}} \right) \cdot \frac{{12}}{7}\]

\[ = \frac{{35}}{8} \cdot \frac{{12}}{7} = \frac{{15}}{2}.\]

d) \(1,9 + \left( {2,51 - 2,13 \cdot 4} \right) - \left( {96 \cdot 2,13 - 99 \cdot 2,51} \right)\)

\( = 1,9 + 2,51 - 2,13 \cdot 4 - 96 \cdot 2,13 + 99 \cdot 2,51\)

\( = \left( {2,51 + 99 \cdot 2,51} \right) - \left( {2,13 \cdot 4 + 96 \cdot 2,13} \right) + 1,9\)

\( = 2,51 \cdot \left( {1 + 99} \right) - 2,13 \cdot \left( {4 + 96} \right) + 1,9\)

\( = 2,51 \cdot 100 - 2,13 \cdot 100 + 1,9\)

\( = 251 - 213 + 1,9\)

\( = 38 + 1,9\)

\( = 39,9.\)