Thực hiện phép tính (tính hợp lí nếu có thể): a) 7/4 - 3/4:- 1/3

a) \(\frac{7}{4} - \frac{3}{4}:\frac{{ - 1}}{3}\)

\( = \frac{7}{4} - \frac{3}{4}.\left( { - 3} \right)\)

\( = \frac{7}{4} + \frac{9}{4}\)

\( = \frac{{16}}{4} = 4\).

b) \(\frac{5}{6} - \left[ {\frac{{ - 4}}{5} - \left( {\frac{1}{3} + \frac{2}{5}} \right)} \right]\)

\( = \frac{5}{6} - \frac{{ - 4}}{5} + \left( {\frac{1}{3} + \frac{2}{5}} \right)\)

\( = \frac{5}{6} + \frac{4}{5} + \frac{1}{3} + \frac{2}{5}\)

\( = \left( {\frac{5}{6} + \frac{1}{3}} \right) + \left( {\frac{4}{5} + \frac{2}{5}} \right)\)

\( = \frac{7}{6} + \frac{6}{5}\)

\( = \frac{{35}}{{30}} + \frac{{36}}{{30}} = \frac{{71}}{{30}}\).

c) \(0,25.\frac{7}{{15}} - 25\% .\frac{{ - 8}}{{15}} + 2,75\)

\[ = 0,25.\frac{7}{{15}} + 0,25.\frac{8}{{15}} + 2,75\]

\[ = 0,25.\left( {\frac{7}{{15}} + \frac{8}{{15}}} \right) + 2,75\]

\[ = 0,25.\frac{{15}}{{15}} + 2,75\]

\[ = 0,25 + 2,75 = 3\].