Question

If $n\left(A\right)=25,n\left(B\right)=35$ and $n(A\cap B)=10$ then find $n(A\cup B)$

Answer 1

$n\left(A\right)=25n\left(B\right)=35$

$n(A\bigcap B)=10$

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

$n(A\bigcup B)=25+35-10$

$=60-10$

$n(A\bigcup B)=50$