Tính hợp lí các biểu thức: (a) -4/12 - (-13/39 - 0,25) + 0,75 (b) 2/5 - (4/3 + 4/5) - (-1/9 - 0,4) + 11/9

a) \( - \frac{4}{{12}}. - \left( { - \frac{{13}}{{39}} - 0,25} \right) + 0,75\)

\( = - \frac{1}{3} + \frac{1}{3} + 0,25 + 0,75 = 1\)

b) \(\frac{2}{5} - \left( {\frac{4}{3} + \frac{4}{5}} \right) - \left( { - \frac{1}{9} - 0,4} \right) + \frac{{11}}{9}\)

\( = \frac{2}{5} - \frac{4}{3} - \frac{4}{5} + \frac{1}{9} + 0,4 + \frac{{11}}{9}\)

\( = \left( {\frac{2}{5} - \frac{4}{5} + 0,4} \right) + \left( {\frac{1}{9} + \frac{{11}}{9} - \frac{4}{3}} \right)\)

\( = \left( {\frac{{2 - 4 + 2}}{5}} \right) + \left( {\frac{{1 + 11 - 12}}{9}} \right)\)

= 0