## Finite Math and Applied Calculus (6th Edition)

"$\cup$" (union of sets)
Looking at the CardinaIity of a Union, If A and $B$ are finite sets, then $n(A\cup B)=n(A)+n(B)-n(A\cap B)$. If A and B are disjoint, their intersection is empty, so, in that case, $n(A\cup B)=n(A)+n(B)$ implying that "$\cup$" (union) could represent "sum" of disjoint sets.