In a class of 30 students, 18 students play cricket, 15 students play football 12 play both the games. How many students in the class don't play both the games?
∪=30, n(C)=18, n(F)=15, n(C∩F)=12
Total no. of students who play football, cricket or both.
⇒n(C∪F)=n(C)+n(F)−n(C∩F)
=18+15−12
=21
∴ No. of students who does not play any game is
i.e., n(C∪F)′=n(∪)−n(C∪F)
=30−21
=9