Since this is a uniform distribution, can we just use symmetry for this, and say that our four numbers will be spaced apart, so they will be on the number line at the following locations:
$\frac{1}{5}$, $\frac{2}{5}$, $\frac{3}{5}$, $\frac{4}{5}$
Therefore, the smallest number is expected to be $\frac{1}{5}$.