Tìm x a. x : 2 / 5 = 3 / 7; b. 6 / 5 - x = 7 / 8

* Hướng dẫn giải

$$\begin{gathered} \mathrm{a}. \mathrm{x} : \frac{2}{5}=\frac{3}{7} \\ \mathrm{x}=\frac{3}{7}\times \frac{2}{5} \\ \mathrm{x}=\frac{6}{35} \end{gathered}$$

$$\begin{gathered} \mathrm{b}. \frac{6}{5}-\mathrm{x}=\frac{7}{8} \\ \mathrm{x}=\frac{6}{5}-\frac{7}{8} \\ \mathrm{x}=\frac{13}{40} \end{gathered}$$