Thực hiện phép tính:
a) \(2\frac{1}{5}:\left( {1\frac{2}{5} + \frac{{ - 3}}{{10}}} \right) - \frac{2}{5};\)
b) \(\frac{{ - 15}}{4}.3\frac{1}{3} - 1\frac{3}{4} + \frac{{ - 7}}{8}\)
Thực hiện phép tính theo thứ tự trong ngoặc, nhân/chia, cộng/trừ.
a)
\(\begin{array}{l}2\frac{1}{5}:\left( {1\frac{2}{5} + \frac{{ - 3}}{{10}}} \right) - \frac{2}{5} = \frac{{11}}{5}:\left( {\frac{7}{5} + \frac{{ - 3}}{{10}}} \right) - \frac{2}{5}\\ = \frac{{11}}{5}:\left( {\frac{{14}}{{10}} + \frac{{ - 3}}{{10}}} \right) - \frac{2}{5} = \frac{{11}}{5}:\frac{{11}}{{10}} - \frac{2}{5}\\ = \frac{{11}}{5}.\frac{{10}}{{11}} - \frac{2}{5} = \frac{{10}}{5} - \frac{2}{5} = \frac{8}{5}.\end{array}\)
b)
\(\begin{array}{l}\frac{{ - 15}}{4}.3\frac{1}{3} - 1\frac{3}{4} + \frac{{ - 7}}{8} = \frac{{ - 15}}{4}.\frac{{10}}{3} - \frac{7}{4} + \frac{{ - 7}}{8}\\ = \frac{{\left( { - 15} \right).10}}{{4.3}} - \frac{7}{4} + \frac{{ - 7}}{8} = \frac{{ - 25}}{2} - \frac{7}{4} + \frac{{ - 7}}{8}\\ = \frac{{ - 100}}{8} + \frac{{ - 14}}{8} + \frac{{ - 7}}{8} = \frac{{ - 121}}{8}\end{array}\)