If $aN = \{ ax:x \in N\} ,$ then the set $3N \cap 7N$ is .....$N$
$21$
$10$
$4$
None of these
If $A=\{3,5,7,9,11\}, B=\{7,9,11,13\}, C=\{11,13,15\}$ and $D=\{15,17\} ;$ find
$A \cap C$
Find the union of each of the following pairs of sets :
$A=\{a, e, i, o, u\} B=\{a, b, c\}$
If $A=\{1,2,3,4\}, B=\{3,4,5,6\}, C=\{5,6,7,8\}$ and $D=\{7,8,9,10\} ;$ find
$A \cup B \cup C$
Which of the following pairs of sets are disjoint
$\{ x:x$ is an even integer $\} $ and $\{ x:x$ is an odd integer $\} $
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
$D-A$