UPSC NDA Math Model Paper 1

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.