Question

If A and B are two disjoint sets, then $n(A\cup B)$ is equal to

• A. n(A)+n(B)
• B. $n\left(A\right)+n\left(B\right)-n(A\cap B)$
• C. $n\left(A\right)+n\left(B\right)+n(A\cap B)$
• D. n(A) n(B)

Answer 1

The correct option is A

n(A)+n(B)

Two sets are disjoint if they do not have a common element in them , i.e., $A\cap B=\varphi$

$\therefore n(A\cup B)=n\left(A\right)+n\left(B\right)$