What is the equivalent to 25 ?

Explanation:
${\displaystyle \frac{a}{b}}$ can be written as ${\displaystyle \frac{an}{bn}}$ so
${\displaystyle \frac{2}{5}=\frac{4}{10}=\frac{80}{200}=\dots }$
Or ${\displaystyle \frac{2n}{5n}}$

Quite a few things actually!
We can look at ${\displaystyle \frac{2}{5}}$ and convert it to a decimal:
${\displaystyle \frac{2}{5}=0.4}$
and a percentage
${\displaystyle \frac{2}{5}=0.4=40\mathrm{\%}}$
We can write different types of operations to arrive at ${\displaystyle \frac{2}{5}}$:
Addition: ${\displaystyle \frac{1}{5}+\frac{1}{5}=\frac{2}{5}}$
Subtraction: ${\displaystyle \frac{4}{5}-\frac{2}{5}=\frac{2}{5}}$
Multiplication: ${\displaystyle 2\times \frac{1}{5}=\frac{2}{5}}$
Division: ${\displaystyle \frac{\frac{1}{5}}{\frac{1}{2}}=\frac{2}{5}}$
We can find fractions that have an equal value to ${\displaystyle \frac{2}{5}}$, such as ${\displaystyle \frac{4}{10}}$ and ${\displaystyle \frac{6}{15}}$.

There are infinitely many numbers which are equivalent to $\frac{2}{5}$
$\frac{2}{5}$ represents a fraction of a whole. It can be expressed as a proper fraction, or a decimal or as a percent.
$\frac{2}{5}=0.4=40\mathrm{\%}$
However $\frac{2}{5}$ is the simplest form of many equivalent fraction.
Recall that multiplying any number by 1 does not change its value.
1 can be written as $\frac{2}{2},\frac{3}{3},\frac{4}{4},\frac{9}{9},\frac{15}{15},\frac{21}{21},\frac{50}{50}...$
If you multiply the top and bottom of a fraction by the same number you do not change its value, only what it looks like.
$\frac{2}{5}\times \frac{2}{2}=\frac{4}{10}$
All the following are fractions equivalent to $\frac{2}{5}$
$\frac{2}{5}=\frac{4}{10}=\frac{6}{15}=\frac{8}{20}=\frac{12}{30}=\frac{20}{50}=\frac{50}{125}=...$
All of these simplify to the decimal 0.4