Taking the set of natural numbers as the universal set, write down the complements of the following sets:

$\{ x:x$ is a positive multiple of $3\} $

Given $n(U) = 20$, $n(A) = 12$, $n(B) = 9$, $n(A \cap B) = 4$, where $U$ is the universal set, $A$ and $B$ are subsets of $U$, then $n({(A \cup B)^C}) = $

If $n(U)$ = $600$ , $n(A)$ = $100$ , $n(B)$ = $200$ and $n(A \cap  B )$ = $50$, then $n(\bar A  \cap \bar B )$ is 

($U$ is universal set and $A$ and $B$ are subsets of $U$)

Fill in the blanks to make each of the following a true statement :

$A \cap A^{\prime}=\ldots$

Let $A$ and $B$ be two sets then $(A \cup B)' \cup (A' \cap B)$ is equal to