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.
(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.