Thực hiện phép tính a) 3/7*(-1/2 +1(1/2)) - 2/7 : 1/4

* Hướng dẫn giải

a) $\frac{3}{7}.(\frac{-1}{2}+1\frac{1}{2})-\frac{2}{7}:\frac{1}{4}$ 

$=\frac{3}{7}.(\frac{-1}{2}+\frac{3}{2})-\frac{2}{7}:\frac{1}{4}$ 

$=\frac{3}{7}.\frac{2}{2}-\frac{2}{7}.\frac{4}{1}$ 

$=\frac{3}{7}-\frac{8}{7}=\frac{3-8}{7}=\frac{5}{7}$ 

b) $\frac{-5}{6}.\frac{7}{13}+\frac{19}{13}:\frac{6}{-5}+\frac{2}{5}$ 

$=\frac{-5}{6}.\frac{7}{13}+\frac{19}{13}.\frac{-5}{6}+\frac{2}{5}$ 

$=\frac{-5}{6}.(\frac{7}{13}+\frac{19}{13})+\frac{2}{5}$ 

$=\frac{-5}{6}.\frac{26}{13}+\frac{2}{5}$ 

$=\frac{-5}{6}.2+\frac{2}{5}$ 

$=\frac{-5}{6}.\frac{2}{1}+\frac{2}{5}$ 

$=\frac{-10}{6}+\frac{2}{5}$ 

$=\frac{-50}{30}+\frac{12}{30}=\frac{-38}{30}$ 

$=\frac{(-38):2}{30:2}=\frac{-19}{15}$