Four Fours/81
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Puzzle
Using exactly $4$ instances of the number $4$, the task is to write an expression for $81$, using whatever arithmetical operations you consider necessary.
Solutions
Solution $1$
- $81 = \dfrac 4 {. \dot 4} \times \dfrac 4 {. \dot 4}$
Solution $2$
- $81 = \paren {\dfrac 4 {. \dot 4} }^{\tfrac 4 {\sqrt 4} }$