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\} $
$A = \{ x:x$ is a natural number and multiple of $3\} = \{ 3,6,9 \ldots \} $
As $B = \{ x:x$ is a natural number less than $6\} = \{ 1,2,3,4,5,6\} $
$A \cup B=\{1,2,4,5,3,6,9,12 \ldots\}$
$\therefore A \cup B = \{ x:x = 1,2,4,5$ or a multiple of $3\} $
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
$D-A$
If $A$ and $B$ are two sets such that $A \subset B$, then what is $A \cup B ?$
Find the union of each of the following pairs of sets :
$A=\{1,2,3\}, B=\varnothing$
If $A = \{ x:x$ is a natural number $\} ,B = \{ x:x$ is an even natural number $\} $ $C = \{ x:x$ is an odd natural number $\} $ and $D = \{ x:x$ is a prime number $\} ,$ find
$C \cap D$
If ${N_a} = \{ an:n \in N\} ,$ then ${N_3} \cap {N_4} = $