100,000 random people were tested for condition a. roberto's doctor told him he tested positive for condition a. if the test is 99% accurate and condition a is rare—one out of every thousand people have it. what is the probability that testing positive means roberto has condition a? 99.0% 1% 9% 99.9%

He would have a 9% of having the rare condition.

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The answer would be: 99.0%

The disease is rare with a prevalence of one out of every thousand people have it. That means, the chance of Roberto has the disease without any test would be 1/1000 or 0.1%
The test sensitivity is 99%, which mean 99% of people with positive test result would have the disease. The chance is should not be influenced by the disease prevalence.