chance of having the disease: 0.1% chance of testing positive: 5% or 0.1% 1 - (0.95 * 0.999) = 0.05095 chance of having the disease given a positive test: 0.001/0.05095 = 0.01963 2% a way to easily estimate it is by imagining 1000 people. expect 50 to 51 positive tests but only 1 person to actually have the disease. (50 or 51 because the person that has the disease could be part of or separate from the false positive group). so the answer if between 1/50 and 1/51 or around 2%
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