Question

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
$C\cap D$

Answer 1

It can be written as
$A$ = {$x:x$ is a natural number} = $\{1,2,3,4,5\dots \}$
$B$ = {$x:x$ is an even natural number} = $\{2,4,6,8\dots \}$
$C$ = {$x:x$ is an odd natural number} = $\{1,3,5,7,9\dots \}$
$D$ = {$x:x$ is a prime number} = $\{2,3,5,7\dots \}$
$C\cap D$ = {$x:x$ is odd prime number}