. Given: - A doctor knows that meningitis causes stiff neck 50% of the time - Prior probability of any patient having meningitis is 1/50,000 - Prior probability of any patient having stiff neck is 1/20 . If a patient has stiff neck, what's the probability he/she has meningitis? P(S| M) P(M) P(M | S) = P(S) Solve this equation for P(M/S)