A certain virus infects one in every 300 people. a test used to detect the virus in a person is positive 80% of the time if the person has the virus and 10% of the time if the person does not have the

A certain virus infects one in every 300 people. a test used to detect the virus in a person is positive 80% of the time if the person has the virus and 10% of the time if the person does not have the virus. (this 10% result is called a false positive.) let a be the event "the person is infected" and b be the event "the person tests positive".