If a randomly selected job applicant is given a drug test, there is a 0.038 probability that the applicant will test positive for drug use (based on data from Quest Diagnostics).

a. If a job applicant is randomly selected and given a drug test, what is the probability that the applicant does not test positive for drug use?

b. Find the probability that when two different job applicants are randomly selected and given drug tests, they both test positive for drugs.

c. If 500 job applicants are randomly selected and they are all given drug tests, find the probability that at least 20 of them test positive for drugs.