Question

Let $n\left(A\right)=28$,$n(A\cap B)=8$, $n(A\cup B)=52$, then $n(A\cap B^{\prime })=$.

• A. $30$
• B. $32$
• C. $20$
• D. none of these

Answer 1

Answer: (C)

$20$

Given $n\left(A\right)=28$,$n(A\cap B)=8$.

We have $A\cap B^{\prime }=A-A\cap B$.

This give $n(A\cap B^{\prime })=n\left(A\right)-n(A\cap B)$

or, $n(A\cap B^{\prime })=28-8=20$.