In a population of 100 persons, 40 persons like tea and 30 persons like coffee. 10 persons like both of them. How many persons like neither tea nor coffee?

Correct Answer: 40
Given, a + b + c + d = 100, a + c = 40, b + c = 30, c = 10 b+10=30 => b=20 a + b + c = 40+20 = 60 d+60=100 => d=40 i.e. 40 persons like neither tea nor coffee.