Thực hiện phép tính (tính hợp lí nếu có thể): a) \(\frac{1}{5} + \frac{{ - 5}}{{19}} + \frac{4}{5} + \frac{{ - 14}}{{19}}.\) b) \(2,35:\left( { - 0,01} \right) + 650 \cdot \left( { - 0,1} \

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

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

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

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

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

\( = \frac{2}{3} \cdot \frac{5}{4} - \frac{5}{4} + \frac{1}{3} \cdot \frac{5}{4}\)

\( = \frac{5}{4} \cdot \left( {\frac{2}{3} - 1 + \frac{1}{3}} \right) = \frac{5}{4} \cdot \left[ {\left( {\frac{2}{3} + \frac{1}{3}} \right) - 1} \right]\)

\( = \frac{5}{4} \cdot \left[ {\frac{3}{3} - 1} \right] = \frac{5}{4} \cdot \left( {1 - 1} \right)\)

\( = \frac{5}{4} \cdot 0 = 0.\)

b) \(2,35:\left( { - 0,01} \right) + 650 \cdot \left( { - 0,1} \right)\)

\( = - 235 - 65\)

\( = - 300.\)

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

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

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

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

\[ = 0.\]