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\} $

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.

If $A=\{1,2,3,4\}, B=\{3,4,5,6\}, C=\{5,6,7,8\}$ and $D=\{7,8,9,10\} ;$ find

$A \cup B$

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 $n(A) = 3$ and $n(B) = 6$ and $A \subseteq B$. Then the number of elements in $A \cap B$ is equal to

Let $A, B$ and $C$ be sets such that $\phi  \ne A \cap B \subseteq C$. Then which of the following statements is not true ?