Question

Suppose we assume that 5% of people are drug users. If a person is a drug...

Suppose we assume that 5% of people are drug users. If a person is a drug user, the result of the test is positive 95% of the time, and if the person is not a drug user, the result is negative 90% of the time. A person is randomly selected. What is the probability that he tests positive for drugs?

Homework Answers

Answer #1

Solution:

Suppose we have 10000 people in total.

The number of drug users are

The positive result for drug users are

The number of non-drug users are

The negative results for non-drug users are

The above information can be put in the below table as:

Positive Negative Total
Drug User 475 25 500
Non-drug User 950 8550 9500
Total 1425 8575 10000

Therefore, the probability that a randomly selected person tests positive for drugs is:

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