Four Fours/91/Solutions/1

Puzzle: Four Fours: $91$

Using exactly $4$ instances of the number $4$, the task is to write an expression for $91$, using whatever arithmetical operations you consider necessary.

Solution

$91 = 4! \times 4 - \dfrac {\sqrt 4} {.4}$

Sources

• 1964: L.H. Clarke: Fun with Figures ... (previous) ... (next): Solutions: $(46)$
• 1980: Angela Dunn: Mathematical Bafflers (revised ed.) ... (previous) ... (next): $1$. Say it with Letters: Algebraic Amusements: Four Fours