Question

In a survey, 2000 people were queried if they read India Today or Business Times. It
was found 1200 read India Today, 900 read Business Times and 400 read both. How
many read at least one magazine

Answer 1

$$P(A\cup B)=P(A)+P(B)-P(A\cap B)$$

How many read at least one magazine

$$1200+900-400=1700$$

1700 people  read at least one magazine.