Question

Use the following results from a test for marijuana​ use, which is provided by a certain drug testing company. Among 140 subjects with positive test​ results, there are 30 false positive results. Among 152 negative​ results, there are 4 false negative results. Complete parts​ (a) through​ (c). (Hint: Construct a​ table.)

a. How many subjects were included in the​ study?

The total number of subjects in the study was

.b. How many subjects did not use​ marijuana?

A total of subjects did not use marijuana.

c. What is the probability that a randomly selected subject did not use​ marijuana?

The probability that a randomly selected subject did not use marijuana is

Answer 1

Based on the data, we create following table

False positive is when tested positive but actually did not use

False negative is when tested negative but actually used

a) As can be seen in the grand total from the table,

The total number of subjects was

b) From the column "Did not use", we get the total = 178

A total of subjects did not use marijuana. =

c) P(randomly selected subject did not use marijuana) = number of subjects who did not use marijuana / total number of subjects.

                = 178/292

                 = 0.6096

The probability that a randomly selected subject did not use marijuana is

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