Tìm x, biết: a) (4,5 - 2x) . 1 4/7 = 11/14 b) x/4 - x/5 = -1 1/2

* Hướng dẫn giải

a) $\left(4,5-2.x\right).1\frac{4}{7}=\frac{11}{14}\Rightarrow 4,5-2.x=\frac{11}{14}:\frac{11}{7}$$\Rightarrow \frac{9}{2}-2.x=\frac{1}{2}\Rightarrow 2.x=\frac{9}{2}-\frac{1}{2}=4\Rightarrow x=2.$

b) $\frac{x}{4}-\frac{x}{5}=-1\frac{1}{2}\Rightarrow x.\left(\frac{1}{4}-\frac{1}{5}\right)=-\frac{3}{2}$$\Rightarrow x.\frac{1}{20}=-\frac{3}{2}\Rightarrow x=\left(-\frac{3}{2}\right).\frac{1}{20}=-\frac{3}{40}.$