Answer
$5$
Work Step by Step
The set $A$ and $B$ and $C$ is $A\cap B\cap C$, is the set of elements that are common to $A$, $B$, and $C$.
Identify the number inside the region that is common to the sets $A$, $B$, and $C$,.
Using the diagram: $n(A\cap B\cap C)=5$.
