HI; I don't understand why but I can get the answer.

On a certain Pacific island, a particular disease is caught by one person in a thousand.98% of those who have the disease respond positively to a diagnostic test, but 3% of thosewho do not have the disease also respond positively to the same test (a ‘false positive’). Ifa person selected at random responds positively to the test, what is the probability thathe actually has the disease?

if 98% have the disease and respond positively to the test and 3% respond positively and do npt have the disease

why aren't their 101% positive.

I got the answer by 98 - 3 = 95 then (95 / 3)/1000 = 0.03166. Don't know why it works.

Thanks.