30% of a population are infected by a virus. A medical test correctly identifies all of the infected people, but only 45% of the healthy people. [3 marks] (a) All people in the population are tested once. What is the percentage of people with positive test? [3 marks] (b) If an individual is tested positive, what is the probability that he has the virus? [4 marks] (c) An individual performs a sequence of independent tests, and all their results are positive. After how many positive tests can he be 80% sure that he has the virus