sets question

Question

two sets P and Q are such that n(P) =7, n(Q)=5 and n(PUQ)=9, then n (PnQ) IS

Answer 1

n(P∩Q) = n(P) + n(Q) - n(PUQ)

 

n(P∩Q) = 7 + 5 - 9

 

n(P∩Q) = 3