In this example? Because we know that one is a true positive. We tested 100 people with a false positive, and 1 with a true positive. If we test again, and the

In this example? Because we know that one is a true positive. We tested 100 people with a false positive, and 1 with a true positive. If we test again, and the test is "fair", then of these 101 people, we will retest 99% (or 99) true negative, 1% (or 1) false positive, and 1 true positive. So two positives, one false positive and one true positive. 1 out of 2 is 50%. (Tho, there is a chance also that the true positive might come back as a false negative, then 1 out of 1 or 100% of positive results would be false positive)