Question

If A and B are not disjoint sets, then $n(A\cup B)$ is equal to

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

Answer 1

The correct option is B

n(A)+n(B)-n(A $\cap$ B)

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