Giải bài 5 trang 32

Đề bài

Thực hiện phép tính:

a) $2\frac{1}{5}:\left(1\frac{2}{5}+\frac{-3}{10}\right)-\frac{2}{5};$

b) $\frac{-15}{4}.3\frac{1}{3}-1\frac{3}{4}+\frac{-7}{8}$

Lời giải chi tiết

a) $2\frac{1}{5}:\left(1\frac{2}{5}+\frac{-3}{10}\right)-\frac{2}{5}$

 $\begin{array}{c}=\frac{11}{5}:\left(\frac{7}{5}+\frac{-3}{10}\right)-\frac{2}{5}\\ =\frac{11}{5}:\left(\frac{14}{10}+\frac{-3}{10}\right)-\frac{2}{5}\\ =\frac{11}{5}:\frac{11}{10}-\frac{2}{5}\\ =\frac{11}{5}.\frac{10}{11}-\frac{2}{5}\\ =\frac{10}{5}-\frac{2}{5}\\ =\frac{8}{5}\end{array}$

b) $\frac{-15}{4}.3\frac{1}{3}-1\frac{3}{4}+\frac{-7}{8}$

 $\begin{array}{c}=\frac{-15}{4}.\frac{10}{3}-\frac{7}{4}+\frac{-7}{8}\\ =\frac{\left(-15\right).10}{4.3}-\frac{7}{4}+\frac{-7}{8}\\ =\frac{-25}{2}-\frac{7}{4}+\frac{-7}{8}\\ =\frac{-100}{8}+\frac{-14}{8}+\frac{-7}{8}\\ =\frac{-121}{8}\end{array}$