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A study considered risk factors for HIV infection among intravenous drug users. It found that 30%...

A study considered risk factors for HIV infection among intravenous drug users. It found that 30% of users who had ≤ 100 injections per month (light users) were HIV positive.

a) What is the probability that exactly 3 out of 15 light users are HIV positive?

b) What is the probability that at least 3 out of 15 light users are HIV positive?

Math   Statistics-And-Probability   
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Answer #1

The number of 15 light users who are HIV positive could be modelled here as:

a) The probability here is computed as:

Therefore 0.1700 is the required probability here.

b) Probability that at least 3 out of 15 are HIV positive is computed here as:

Therefore 0.8732 is the required probability here.

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