Question

results from a marijuana drug test study showed 143 subjects with positive test results including 24 false positive results. there were 157 negative results, including 3 false negative results. what is the probability that a randomly selected subject did not use marijuana? a. 0.523 b. 0.477 c. 0.593 d. 0.533

Explanation:

Step1: Calculate total number of subjects

The total number of subjects is the sum of positive - test subjects and negative - test subjects. So, $143 + 157=300$.

Step2: Calculate number of non - users

The number of non - users is the sum of false positives and true negatives. True negatives are $157 - 3=154$, and false positives are 24. So the number of non - users is $154 + 24 = 178$.

Step3: Calculate the probability

The probability $P$ that a randomly selected subject did not use marijuana is the number of non - users divided by the total number of subjects. So, $P=\frac{178}{300}\approx0.593$.

Answer:

c. 0.593