B. 20
Feedback number of boys who like at least 1 thing = 60 – 5 = 55
Now, let number of students who like pizza = P(a) and number of students who like burger = P(b) and number of those who like both = P(a ∩ b) =?
Hence we have
⇒ 55 = P(a) + P(b) - P(a ∩ b)
⇒ 55 = 45 + 30 - P(a ∩ b)
⇒ P(a ∩ b) = 75 – 55 = 20