Let $y(t)=x(4t)$, where $x(t)$ is a continuous–time periodic signal with fundamental period $100~\text{s}$. The fundamental period of $y(t)$ is _______ s (rounded off to the nearest integer).
Show Hint
For $x(at)$, time is {compressed} by $a$; period shrinks by the same factor: $T/ a$.
Time–scaling rule. If $x(t)$ has fundamental period $T_0$, then $x(at)$ has fundamental period $T_0/|a|$.
Here $a=4$ and $T_0=100~\text{s}$, so
\[
T_y=\frac{T_0}{|a|}=\frac{100}{4}=25~\text{s}.
\]