Tính hợp lí (nếu có thể): b) ( 1 + 2/ 3 − 1 /4 ) ( 0 , 8 − 3 /4 ) ^2 ;

b) \(16\frac{2}{7}:\left( {\frac{{ - 3}}{5}} \right) + 28\frac{2}{7}:\frac{3}{5}\)

\( = 16\frac{2}{7} \cdot \left( {\frac{{ - 5}}{3}} \right) + 28\frac{2}{7} \cdot \frac{5}{3}\)

\( = \frac{5}{3}\, \cdot \,\left( { - 16\frac{2}{7} + 28\frac{2}{7}} \right)\)\( = \frac{5}{3}\, \cdot \,12\)\( = 20\).