Question

Let $A$ and $B$ be two finite sets such that $n\left(A\right)=20$, $n\left(B\right)=28$ and $n(A\cup B)=36$, find $n(A\cap B)$. <!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->

• A. 18
• B. 14
• C. 12
• D. 10

Answer 1

The correct option is C 12

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

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

= 20 + 28 - 36

= 12