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

Let $A = \{a, b, c\}, B = \{b, c, d\}, C = \{a, b, d, e\},$ then $A \cap (B \cup C)$ is

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

$D-A$

Which of the following pairs of sets are disjoint 

$\{ x:x$ is an even integer $\} $ and $\{ x:x$ is an odd integer $\} $

Find the union of each of the following pairs of sets :

$A = \{ x:x$ is a natural number and $1\, < \,x\, \le \,6\} $

$B = \{ x:x$ is a natural number and $6\, < \,x\, < \,10\} $

Let $A$ and $B$ be two sets. Then