Question

If $n\left(A\right)=n\left(B\right),$ then which of the following is correct?

• A. $n(A–B)=n(B–A)$
• B. $n(A\cup B)=n\left(A\right)+n\left(B\right)$
• C. $n(A\cap B)=n\left(B\right)+n(A–B)$
• D. $n(A–B)=n(A\cap B)$

Answer 1

The correct option is A $n(A–B)=n(B–A)$

Checking all the option, we get
$n(A–B)=n(B-A)$
$n(A\cup B)=n\left(A\right)+n\left(B\right)-n(A\cap B)$
$n(A\cap B)=n\left(A\right)+n\left(B\right)-n(A\cup B)$
$n(A–B)=n\left(A\right)-n(A\cap B)$