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It is given that only 0.1% of a large population have COVID infection. In this population, the reliability of COVID RTPCR-test is specified as follows :

For persons having COVID, 90% of the test detects the disease but 10% goes undetected. For persons not having COVID, 99% of the test is judged COVID negative but 1% are diagnosed as COVID positive.

It is given that only 0.1% of a large population have COVID infection. In this population, the reliability of COVID RTPCR-test is specified as follows :

For persons having COVID, 90% of the test detects the disease but 10% goes undetected. For persons not having COVID, 99% of the test is judged COVID negative but 1% are diagnosed as COVID positive.

Based on the above informations, answer the question :

The probability that the selected person will be diagonosed as COVID positive is :

Solution

✅ Correct Option: 4

P(positive)=P(positive∣COVID)P(COVID)+P(positive∣no COVID)P(no COVID)=0.9(0.001)+0.01(0.999)=0.0009+0.00999=0.01089=1089100000P(\text{positive}) = P(\text{positive}|\text{COVID})P(\text{COVID}) + P(\text{positive}|\text{no COVID})P(\text{no COVID}) = 0.9(0.001) + 0.01(0.999) = 0.0009 + 0.00999 = 0.01089 = \frac{1089}{100000}.

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