Question

Let $n(A-B)=25+x$, $n(B-A)=2x$ and $n(A\cap B)=2x$. If n(A) = 2(n(B)) then 'X' is

• A. 4
• B. 5
• C. 6
• D. 7

Answer 1

The correct option is B

5

$n(A-B)=25+x,n(B-A)=2x$

$n(A\cap B)=2x$

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

$=25+x+2x=25+3x$

$n\left(B\right)=n(B-A)+n(A\cap B)=2x+2x=4x$

$n\left(A\right)=2n\left(B\right)\Rightarrow 25+3x=2\left(4x\right)$

$\Rightarrow 5x=25\Rightarrow x=5$