I'm doing the practice test for a stats class and I'm stuck on a question.
A special test is given to people complaining of severe headaches. If someone has a brain tumor, the test is positive with a probability of .85(85%) If they have no tumor, the test is positive with a probability of .1(10%) Only 4%(.04) of those tested actually have brain tumors.
Whats is the probability that someone who tested positive has a brain tumor?
The answer is 0.262, but I have no idea how to get to that answer.
At first they ask "what is the probability someone random selected from those who take the test has a brain tumor AND test positive?"
For that I multiplied .85 by .04 and got the correct answer of 0.034