Tìm x, biết:

- Hướng dẫn giải

Ta có:

$\begin{array}{l}\left(1\frac{4}{7}-\mathrm{x}\right):\left(0,5-\frac{5}{21}\right)=2\frac{8}{11}\\ \left(\frac{11}{7}-\mathrm{x}\right):\left(\frac{1}{2}-\frac{5}{21}\right)=\frac{30}{11}\\ \frac{11}{7}-\mathrm{x}=\frac{30}{11}.\frac{11}{42}\\ \frac{11}{7}-\mathrm{x}=\frac{5}{7}\\ \mathrm{x}=\frac{11}{7}-\frac{5}{7}=\frac{6}{7}\end{array}$