I have two inequalities ($a,b,c,d,e > 0$):
$$\begin{array}{lcl}
a & \le & b \\
\frac{1}{c} & \le & \frac{d}{e}
\end{array}
$$
why it is correct to consider the product of the element on the same side?
$$ \frac{a}{c} \le b \cdot \frac{d}{e}$$
Please, can you help me? Thanks!