Probability

In a flu epidemic 45% of people have sore throat.if a person has a sore throat the probability of not having flu is 0.4 if a person does not have a sore throat the probability of having flu is 0.2 calculate the probability that a person chosen at random has flu

 

He has a 45% chance of having a sore throat AND if he has a sore throat he has 0.6 chance of having the flu

that is 0.45*0.6 = 0.27

 

He has a 55% chance of NOT having a sore throat and given that he does not have a sore throat he still has 0.2 chance of having flu

that is 0.55*0.2 = 0.11

 

so that is    0.27+0.11 = 0.38

 

A person chosen at random has a 38% chance of having the flu.

 

WOW that is a lot of sick people - I am not going there!