Question

If $n\left(A\right)=29,n(A\cup B)=15,n(A\cap B)=7$ find $n\left(B\right)$.

Answer 1

Given $n\left(A\right)=29,n(A\cup B)=15,n(A\cap B)=7$

As we know that

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

$⟹n\left(B\right)=n\left(A\right)-n(A\cup B)-n(A\cap B)=29-15-7=7$