Question

The following data summarizes results from 1000 ​pre-employment drug screening tests. If one of the test subjects is randomly​ selected, find the probability that the subject had a positive test result or a negative test result.

Positive Test Result Negative Test Result
Subject Uses Drugs 76 6
Subject Is Not a Drug User 95 823
P (subject had a positive test result or a negative test result)= simplify your answer.

Answer 1

P (subject had a positive test result or a negative test result) = 1

Explanation:

Given

The table above

Required

P (subject had a positive test result or a negative test result)

This is calculated as follows;

P (subject had a positive test result or a negative test result) =

P (subject had a positive test result) + P (subject had a negative test result)

Calculating P (subject had a positive test result)

This can be calculated by number of subjects with positive results divided by 1000

Only data from the column of subjects with positive results will be considered.

Number of Subjects = Subjects that uses drugs + Subjects that do not use drugs

Number of subjects = 76 + 95

Number of Subjects = 171

P (Subject had a positive test Result) = 171/1000

Calculating P (subject had a negative test result)

This can be calculated by number of subjects with negative results divided by 1000

Only data from the column of subjects with negative results will be considered.

Number of Subjects = Subjects that uses drugs + Subjects that do not use drugs

Number of subjects = 6 + 823

Number of Subjects = 829

P (Subject had a negative test Result) = 829/1000

Hence, P (subject had a positive test result or a negative test result) =

P (subject had a positive test result) + P (subject had a negative test result) = 171/1000 + 829/1000

P (subject had a positive test result or a negative test result) = (171 + 829)/1000

P (subject had a positive test result or a negative test result) = 1000/1000

P (subject had a positive test result or a negative test result) = 1