Answer:
The probability is 12.66%.
This is a low probability, so it is unlikely for such a combined sample to test positive.
Step-by-step explanation:
If the probability of being infected is 0.005, the probability of not being infected is 0.995.
Then, to find the probability of at least one of the 27 people being infected P(A), we can find the complementary case: all people are not infected: P(A').
Then we can find P(A) using:
This is a low probability, so it is unlikely for such a combined sample to test positive.