Question

If $A=\{1,2,3\}$ and $B=\{3,4\},$ then $n(A-B)+n(A\times B)$ is

Answer 1

$A-B=\{1,2\}$
$n(A-B)=2$
$n(A\times B)=n\left(A\right)\times n\left(B\right)$
$=3\times 2=6$
$\therefore n(A-B)+n(A\times B)=2+6=8$