Question

For two sets $A$ and $B$ , if $n\left(A\right)=20,n\left(B\right)=18$ and $n\left(A\cap B\right)=5$ , then $n\left(A-B\right)$ is equal to

• A. $13$
• B. $12$
• C. $15$
• D. $18$

Answer 1

Answer: (C)

$n\left(A-B\right)=n\left(A\cup B\right)-n\left(B\right)=n\left(A\right)-n\left(A\cap B\right)$
$=20-5$
$=15$