Q.

In a group of 80 students, 50 play football, 45 play cricket and each student plays either football or cricket. Find the number of students who play both the games.

1 12  
2 14  
3 15  
4 18  

Ans.

(3)

Let F be the set of the students who play football and C be the set of students who play cricket.

Then n(F)=50 and n(C)=45.

Since each of the 80 students play atleast one of the two games,

we have n(F∪C)=80.

n(F∩C)=n(F)+n(C)-n(F∪C)=50+45-80=15.