Question

Let A and B be two sets such that n(A) =20 , $n(A\cup B)=42$ nd $n(A\cap B)=4$ Find n(B), n(A-B) and n(B-A)

Answer 1

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

$n\left(B\right)=42-20+4=26$

$n(A-B)=n\left(A\right)-n(A\cap B)=20-4=16$

$n(B-A)=n\left(B\right)-n(A\cap B)=26-4=22$