If $A=\{3,5,7,9,11\}, B=\{7,9,11,13\}, C=\{11,13,15\}$ and $D=\{15,17\} ;$ find

$A \cap D$

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

$A=\{a, e, i, o, u\} B=\{a, b, c\}$

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\} $

Find the intersection of each pair of sets :

$X=\{1,3,5\} Y=\{1,2,3\}$

If $A, B, C$ be three sets such that $A \cup B = A \cup C$ and $A \cap B = A \cap C$, then

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

$B \cup C \cup D$