Let A be the set of people who like coffee and B be the set of people who like tea. Given that n(A)=37,n(B)=52 and n(A∪B)=70 Since, every person likes at least one drink ( 0 elements outside A and B), we have: n(A∪B)=n(A)+n(B)−n(A∩B) ⇒70=37+52−n(A∩B) ⇒n(A∩B)=89−70=19 People who like coffee and NOT tea is given by n(A−B)=n(A)−n(A∩B)=37−19=18.