Tìm y, biết:

* Hướng dẫn giải

a) y + $\frac{3}{4}= \frac{13}{8}$

 $$\begin{gathered} y=\frac{13}{8}-\frac{3}{4} \\ y= \frac{13}{8}-\frac{6}{8} \\ y=\frac{7}{8} \end{gathered}$$

b) y$\times \frac{3}{4}=\frac{9}{40}$

$$\begin{gathered} y=\frac{9}{40}:\frac{3}{4} \\ y= \frac{9}{40}\times \frac{4}{3} \\ y= \frac{36}{120} \\ y=\frac{3}{10} \end{gathered}$$