Question

If $n\left(A\right)=40,n\left(B\right)=27$ and $n(A$ $\cap$ $B)=15$, find $n\left[\right(A$ $\cup$ $B)-A]$

Answer 1

Given, $n\left(A\right)=40,n\left(B\right)=27$ and $n(A\cup B)=15$

From the figure, $(A\cup B)-A$ is the region of " ONLY B "
Hence, $n\left(\right(A\cup B)-A)=n\left(onlyB\right)$

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

$=27-15$

$=12$