Four Fours/81/Solutions/1

Puzzle: Four Fours: $81$

Using exactly $4$ instances of the number $4$, the task is to write an expression for $81$, using whatever arithmetical operations you consider necessary.

Solution

$81 = \dfrac 4 {. \dot 4} \times \dfrac 4 {. \dot 4}$

Sources

• 1964: L.H. Clarke: Fun with Figures ... (previous) ... (next): Solutions: $(46)$