# False Positive

You are tested for a rare flesh-eating virus that afflicts 1% of the population. If you have the virus, the test will always come back positive, but if you do not, there is a 20% chance of a false positive. You are told that your test came back positive. What is the probability that you have the disease?

### 4 guesses to False Positive

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• kelly kreps

20%

• Dude

No, keep guessing.

• Eliza Beth

5%

• Dude

5% is correct, Eliza Beth.

n=100 was used and numbers are rounded to whole people.

Of 100 people, 1 true positive and 20 false positive results are reported.

A total of 21 positives are reported and thus, 1/21 positives are true positives.

1/21 x 100% = 5%

That is the answer, of the 21 positive results, he has a 5% chance of being one of the fortunate 20.

Great job! You’re today’s winner.