Question

$n\left(A\right)=4$ and $n\left(B\right)=5$: $n(A\times B)=$

• A. $20$
• B. $10$
• C. $30$
• D. None of the above

Answer 1

The correct option is A $20$

If $n\left(A\right)=m$,and $n\left(B\right)=n$,then $n(A\times B)=mn$

so$n(A\times B)=5.4=20$