Four Fours/13/Mistake

Source Work

1980: Angela Dunn: Mathematical Bafflers (revised ed.):

Four Fours

Solution

Mistake

The writer added the following postscript: "Another simple solution for $13$ is: $13 = \dfrac {4!} 4 + \dfrac 4 4$."

In fact $\dfrac {4!} 4 + \dfrac 4 4 = 7$.

It is probable that the above is a misprint for this solution:

$13 = \dfrac {4!} {\sqrt 4} + \dfrac 4 4$

Sources

• 1980: Angela Dunn: Mathematical Bafflers (revised ed.) ... (previous) ... (next): $1$. Say it with Letters: Algebraic Amusements: Four Fours