Answer
true.
Work Step by Step
$A'$ represents the elements of the universal set that are not in $A$.
Since $A' \cup A = U$ and $A$ and $A'$ have no common elements, then
$n(U)= n(A')+ n(A)$
Therefore,
$n(A') = n(U) - n(A)$
Thus, the given statement is true.
