Answer
$\not\in$
Work Step by Step
The symbol $\in$ means that the number is an element of the set.
The symbol $\not\in$ means that the number is NOT an element of the set.
Since {$5$} is a set containing its only element $5$, {$5$} is not an element of the set {$3, 4, 5, 6, 7$}. The missing symbol in the blank is $\not\in$
