In a certain population, 0.1% of people are infected by HIV virus. A test is proposed to determine the virus carriers. For an infected person, the test gives positive result in 99% of cases; for an uninfected person, the test gives positive result in 1% of cases. What is the probability of a false positive? (That is, if he test gives positive result, what is the probability that the tested person is actually not infected?) What is the probability of a false positive after two independent positive tests?