Question

If $A=\{5,6,7\},B=\{1,2,3,4\}$, then number of elements in set $(A-B)\times B$ is

Answer 1

Given: $A=\{5,6,7\},B=\{1,2,3,4\}$

$A\cap B=\varphi \Rightarrow A-B=A$

$n\left(\right(A-B)\times B)$

$=n\left(A\right)\cdot n\left(B\right)$

$=3\cdot 4=12$