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) \(\left( {\frac{1}{3} - \frac{3}{{10}}} \right).\frac{5}{3} + \left( {\frac{2}{3} - \frac{7}{{10}}} \right).\frac{5}{3}\)

\( = \frac{5}{3}.\left( {\frac{1}{3} - \frac{3}{{10}} + \frac{2}{3} - \frac{7}{{10}}} \right)\)

\( = \frac{5}{3}.\left[ {\left( {\frac{1}{3} + \frac{2}{3}} \right) + \left( { - \frac{3}{{10}} - \frac{7}{{10}}} \right)} \right]\)

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

\( = \frac{5}{3}.0 = 0\).

c) \(25\%  - 1\frac{1}{2} - {\left( { - \frac{1}{2}} \right)^2} + 0,25:\frac{1}{{12}}\)

\( = \frac{1}{4} - \frac{3}{2} - \frac{1}{4} + \frac{1}{4}.12\)

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

\( =  - \frac{3}{2} + \frac{6}{2}\)

\( = \frac{3}{2}\).