Thực hiện phép tính (tính hợp lí nếu có thể): a) \(\frac{1}{5} + \frac{{ - 5}}{{19}} + \frac{4}{5} + \frac{{ - 14}}{{19}}.\)      b) \(\left( { - 1,6} \right) \cdot \left( { - 0,125} \right

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) \(\left( { - 1,6} \right) \cdot \left( { - 0,125} \right) \cdot \left( { - 0,5} \right)\)

\( = 0,2 \cdot \left( { - 0,5} \right)\)

\( =  - 0,1.\)

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) \[25\%  - 1\frac{1}{2} - {\left( { - \frac{1}{2}} \right)^2} + 0,75:\frac{1}{2}\]

\[ = \frac{1}{4} - \frac{3}{2} - \frac{1}{4} + \frac{3}{4} \cdot 2\]

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

\[ = 0 + \left( { - \frac{3}{2} + \frac{3}{2}} \right)\]

\[ = 0.\]