UPSC NDA 2 2019 Mathematics Solved Paper

Let A = cricket player and B = football player
Then, n(A) = 50%, n(B) = 40%,
n(A∪B)=10%
∴n(A∪B)=n(A)+n(B)–n(A∩B)
=50+40–10
=90–10=80%
∴ per cent of students play either cricket or football = 80%
∴ per cent of students play neither cricket nor football
=100−n(A∪B)
=100−80%=20%