Tính a) 2/5 + 3/5 : (3/5 + -2/3) - 3 1/2 b) 1,25 : 15/20 + (25% - 5/6) : 4 2/3

* Hướng dẫn giải

a) $\frac{2}{5}+\frac{3}{5}:\left(\frac{3}{5}+\frac{-2}{3}\right)-3\frac{1}{2}=\frac{2}{5}+\frac{3}{5}:\frac{-1}{15}=\frac{2}{5}-9=\frac{-43}{5}$

b) $1,25:\frac{15}{20}+\left(25\%-\frac{5}{6}\right):4\frac{2}{3}=\frac{5}{4}.\frac{4}{3}+\left(\frac{1}{4}-\frac{5}{6}\right):\frac{14}{3}$$=\frac{5}{3}+\frac{-7}{12}.\frac{3}{14}=\frac{37}{24}$