SOLUTION: A certain virus infects one in every 400 people. A test used to detect the virus in a person is positive 90% of the time if the person has the virus and 10% of the time if the pers

Question 1050947: A certain virus infects one in every 400 people. A test used to detect the virus in a person is positive 90% of the time if the person has the virus and 10% of the time if the person does not have the virus. Let A be the event "the person is infected" and B be the event "the person tests negative."
(a) Find the probability that a person has the virus given that they have tested positive.

(b) Find the probability that a person does not have the virus given that they have tested negative.
Answer by EliteCracker(4) (Show Source): You can put this solution on YOUR website!
90% of 100% = 9/10
Answer to part A is .
10% of 100% = 1/10
Answer to part B is
CHECK
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90% of 400 = 360 infected people
360/400 = 9/10
Every 9 of 10 people are infected.
10% of 400 = 40 infected people
40/400 = 1/10
Every 1 of 10 people are not infected.
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