Question

If two sets $A$ and $B$ are such that $n\left(A\right)=20$, $n(A\cap B)=4$, and $n(A\cup B)=42$, then

• A. $n\left(B\right)=22$
• B. $n(B-A)=22$
• C. $n\left(B\right)=24$
• D. $n(A-B)=18$

Answer 1

The correct option is B $n(B-A)=22$

$n\left(A\right)=20,n(A\cap B)=4,n(A\cup B)=42$
$\therefore n\left(B\right)=26$,
$n(B-A)=22$,
and $n(A-B)=16$