[tex]\displaystyle \\
x= 40\% ~\text{din}~ y \\ \\
x = 40\% \times y \\ \\
x = \frac{40}{100} \times y \\ \\
x= 0,4y \\ \\
\text{Aflam cat la suta reprezinta numarul y din x} \\ \\
y = \frac{y}{x} \cdot 100 = \frac{y}{0,4y} \cdot 100=\frac{1}{0,4} \cdot 100=2,5 \cdot 100 = \boxed{250\% ~\text{din }~ x}
[/tex]
