A large group of people is to be checked for two common symp

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).

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