Question

Let $A=\{1,2,3\},B=\{4,5,6,7,8\},$ $C=\{4,6,8,10,12\},$ then $n\left[\right(A\times B)-(A\times C\left)\right]=$

Answer 1

$A=\{1,2,3\},B=\{4,5,6,7,8\},$ $C=\{4,6,8,10,12\}$

$(A\times B)-(A\times C)=A\times (B-C)(B-C)=\{5,7\}$

$n\left[\right(A\times B)-(A\times C\left)\right]=n(A\times (B-C\left)\right)=n\left(A\right)\times n(B-C)=3\times 2$
$=6$