Answer :

Solution :

Each student watched either only one film or all three.

Let a = students who watched only A,

b = students who watched only B,

c = students who watched only C,

x = students who watched A, B and C i.e. all three

P(A) = 13, P(B) = 16, P(C) = 19

a + x = 13

b + x = 16

c + x = 19

a + b + c + 3x = 13 + 16 + 19

a + b + c + 3x = 48

Total strength of class is 40,

a + b + c + x = 40

⇒ 2x = 8

x = 4

So 4 students watched all three films.