2000 applicants aged 18-25.
Drug users non-drug users
Positive test results 297 34
Negative test results 3 1666

An applicant has positive test results?

An applicant tests positive and uses drugs?

An applicant tests negative given that the person does use drugs?

An applicant does not use drugs given that the person has a positive test result?

I computed all of my answers over 2000. Is this wrong and why?

Add up each row and each column first.

I assume you want probabilities.

Positive: 331/2000
Positive and uses: 297/2000
Negative, given uses: 3/300
Doesn't use, given positive: 34/331