Four Fours/Lemmata/One Four/4 Tenths/Solutions

Puzzle: One Four: $\dfrac 4 {10}$

Using exactly $1$ instance of the number $4$, the task is to write an expression for $\dfrac 4 {10}$, using whatever arithmetical operations you consider necessary.

Solutions

Solution $1$

$\dfrac 4 {10} = .4$