Tìm x, biết: a) -1/10 + 2/5 x + 7/20 = 1/10 b) 1/3 + 1/2 : x = -1/5

* Hướng dẫn giải

$\begin{array}{l}a)\frac{-1}{10}+\frac{2}{5}x+\frac{7}{20}=\frac{1}{10}\\ \frac{2}{5}x=\frac{1}{10}-\frac{7}{20}+\frac{1}{10}\\ \frac{2}{5}x=-\frac{3}{20}\\ x=-\frac{3}{8}\end{array}$

$\begin{array}{l}b)\frac{1}{3}+\frac{1}{2}:x=-\frac{1}{5}\\ \frac{1}{2}:x=-\frac{1}{5}-\frac{1}{3}\\ \frac{1}{2}:x=-\frac{8}{15}\\ x=-\frac{15}{16}\end{array}$