Tìm x biết a) 1/4 -x = 1/20 + (-2) b) -2/5 -x = 4/15 + -1/3

* Hướng dẫn giải

a) 

$\begin{array}{l}\frac{1}{4}-x=\frac{1}{20}+(-2)\\ \frac{1}{4}-x=\frac{-39}{20}\\ x=\frac{1}{4}-\frac{-39}{20}=\frac{5}{20}+\frac{39}{20}=\frac{44}{20}=\frac{11}{5}\end{array}$

b) 

$\begin{array}{l}\frac{-2}{5}-x=\frac{4}{15}+\frac{-1}{3}\\ \frac{-2}{5}-x=\frac{-1}{15}\\ x=\frac{-2}{5}-\frac{-1}{15}=\frac{-6}{15}-\frac{-1}{15}=\frac{-5}{15}=\frac{-1}{3}\end{array}$