If $A$ and $B$ are disjoint, then $n(A \cup B)$ is equal to
$n(A)$
$n(B)$
$n(A) + n(B)$
$n(A)\,.\,n(B)$
If $A = \{ x:x$ is a natural number $\} ,B = \{ x:x$ is an even natural number $\} $ $C = \{ x:x$ is an odd natural number $\} $ and $D = \{ x:x$ is a prime number $\} ,$ find
$A \cap C$
If $A=\{3,6,9,12,15,18,21\}, B=\{4,8,12,16,20\},$ $C=\{2,4,6,8,10,12,14,16\}, D=\{5,10,15,20\} ;$ find
$D-C$
Is it true that for any sets $\mathrm{A}$ and $\mathrm{B}, P(A) \cup P(B)=P(A \cup B) ?$ Justify your answer.
If $S$ and $T$ are two sets such that $S$ has $21$ elements, $T$ has $32$ elements, and $S$ $\cap \,T$ has $11$ elements, how many elements does $S\, \cup$ $T$ have?
If $A=\{1,2,3,4\}, B=\{3,4,5,6\}, C=\{5,6,7,8\}$ and $D=\{7,8,9,10\} ;$ find
$A \cup B$