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

$B \cup D$

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

$A \cup C$

If the sets $A$ and $B$ are defined as $A = \{ (x,\,y):y = {1 \over x},\,0 \ne x \in R\} $ $B = \{ (x,y):y =  – x,x \in R\} $, then

If $A$ and $B$ are disjoint, then $n(A \cup B)$ 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.