Question

If $n\left(\xi \right)$ $=30,n\left(A\right)=22,n\left(B\right)=15$ and $n(A$ $\cup$ $B)=25$, then find : $n(A$${}^{\prime }$).

Answer 1

Given,

$n($$\xi$$)=30$

$n\left(A\right)=22$

$n\left(B\right)=15$

$n(A$ $\cup$ $B)=25$

$n($$A^{\prime }$$)=$ $n(\xi$)$-n\left(A\right)$

$=30-22$

$=8$