Thực hiện phép tính (tính hợp lí nếu có thể): a) 1/5 + - 5/19 + 4/5 + - 14/19

a) \(\frac{1}{5} + \frac{{ - 5}}{{19}} + \frac{4}{5} + \frac{{ - 14}}{{19}}\)

\( = \left( {\frac{1}{5} + \frac{4}{5}} \right) + \left( {\frac{{ - 5}}{{19}} + \frac{{ - 14}}{{19}}} \right)\)

\( = \frac{5}{5} + \frac{{ - 19}}{{19}}\)

\( = 1 + \left( { - 1} \right) = 0.\)

b) \(\left( { - 0,4} \right) \cdot \left( { - 0,5} \right) \cdot \left( { - 0,8} \right)\)

\[ = 0,2 \cdot \left( { - 0,8} \right)\]

\[ = - 0,16.\]

c) \(\frac{{ - 3}}{5}:\frac{7}{5} - \frac{3}{5}:\frac{7}{5} + 2\frac{3}{5}\)

\( = \frac{{ - 3}}{5} \cdot \frac{5}{7} - \frac{3}{5} \cdot \frac{5}{7} + 2 + \frac{3}{5}\)

\[ = \frac{5}{7} \cdot \left( {\frac{{ - 3}}{5} - \frac{3}{5}} \right) + 2 + \frac{3}{5}\]

\[ = \frac{5}{7} \cdot \frac{{ - 6}}{5} + 2 + \frac{3}{5}\]

\[ = \frac{{ - 6}}{7} + 2 + \frac{3}{5}\]

\[ = \frac{{ - 30}}{{35}} + \frac{{70}}{{35}} + \frac{{21}}{{35}}\]

\[ = \frac{{61}}{{35}}.\]

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

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

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

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

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

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

\( = 38 + 1,9\)

\( = 39,9.\)