Use the following results from a test for marijuana use prov

Use the following results from a test for marijuana use, provided by a drug testing company. Among 155 subjects with positive test results, there are 26 false positive results. Among 162 negative results, there are 10 false negative results. If one of the test subjects is randomly selected, find the probability that the subject tested negative or did not use marijuana. (hint: construct a table)

Please explain how you got the answer.

Solution

Total number of subjects = 155+162 = 317

P(Subject tested positive and did use marijuana) = 129/317

P(Subject tested negative or did not use marijuana) = 1 - P(Subject tested positive and did use marijuana)

P(Subject tested negative or did not use marijuana) = 1 - 129/317 = 188/317 = 0.5931