I am thinking 88% of 1% plus 3% of 99% will test positive for the drug.

The idea being that 1% of people actually use drugs and 88% of the time these people will test positive, while 99% of people do not use drugs and 3% of the time they will test positive.

.88*.01 + .03*.99 = .0385

.01 is 25.97% of .0385

So there is a 25.97% chance that a person testing positive actually did take the drug. What do you think?