Thực hiện phép tính (hợp lý nếu có thể)     a) 2/5 + 3/5                     b) [(1/3) ^2] ^2                c) (1/2)^2 - 1 2/5 . 1/3 +8/3 -2 . 7/5

\({\rm{ a) }}\)\(\frac{2}{5} + \frac{3}{5} = \frac{5}{5} = 1\);

b)\({\left[ {{{\left( {\frac{1}{3}} \right)}^2}} \right]^2} = {\left( {\frac{1}{9}} \right)^2} = \frac{1}{{81}}\);
c) \({\left( {\frac{1}{2}} \right)^2} - \left[ {1\frac{2}{5}.\frac{1}{3} + \left( {\frac{8}{3} - 2} \right).\frac{7}{5}} \right] = \frac{1}{4} - \left[ {\frac{7}{5}.\frac{1}{3} + \left( {\frac{8}{3} - \frac{6}{3}} \right).\frac{7}{5}} \right]\)

\( = \frac{1}{4} - \left[ {\frac{7}{{15}} + \frac{2}{3}.\frac{7}{5}} \right]\)\( = \frac{1}{4} - \left[ {\frac{7}{{15}} + \frac{{14}}{{15}}} \right] = \frac{1}{4} - \frac{7}{5} = \frac{5}{{20}} - \frac{{28}}{{20}} = \frac{{ - 23}}{{20}}\).