Question

If $A$ has $2$ elements and $B$ has $2$ elements, then the number of elements in $A\times B$ is :

Answer 1

Cartesian product of sets contains ordered pair of elements of both sets.

Suppose $A=\{x,y\}$ and $B=\{a,b\}$
Then $A\times B=\left\{\right(x,a),(x,b),(y,a),(y,b\left)\right\}$
Then the number of elements in the above set is $4$.