If $aN = \{ ax:x \in N\} ,$ then the set $3N \cap 7N$ is .....$N$
$21$
$10$
$4$
None of these
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
$C-B$
Find the union of each of the following pairs of sets :
$A = \{ x:x$ is a natural number and multiple of $3\} $
$B = \{ x:x$ is a natural number less than $6\} $
If $A=\{3,5,7,9,11\}, B=\{7,9,11,13\}, C=\{11,13,15\}$ and $D=\{15,17\} ;$ find
$\left( {A \cap B} \right) \cap \left( {B \cup C} \right)$
If $A, B$ and $C$ are any three sets, then $A -(B \cup C)$ is equal to
State whether each of the following statement is true or false. Justify you answer.
$\{a, e, i, o, u\}$ and $\{a, b, c, d\}$ are disjoint sets.