A large group of people is to be checked for two common symptoms of a certain disease. It is thought that 20% possess symptom A alone; 30% possess symptom B alone 10% possess both the remainder have neither symptoms If one person chosen at random from this group, find the conditional probability P(A | B). Solution P(A and B) = 0.1 P(B) = 0.3 so P(A/B) = P(A and B) / P(b) = 0.1/0.3 = 1/3.