Final answer:
The probability that exactly 3 of 5 light users are HIV positive cannot be determined without the prevalence rate of HIV among the light user population. An assumption or estimation based on available data is necessary to perform a probability calculation.
Step-by-step explanation:
The question asks about the probability that exactly 3 out of 5 light users are HIV positive. It is essential to have information about the prevalence of HIV among the population being considered to calculate this probability. However, since the question does not provide a specific prevalence rate for light users, we would need to assume a prevalence rate or have more context to proceed with an accurate calculation.
Without the prevalence rate, one approach could be to use the general HIV prevalence rates from the provided data as a rough estimate for calculation. For example, if we were to assume the light users are in a geographic region with an HIV prevalence of 0.5%, we could apply the binomial probability formula for n=5 (number of trials), k=3 (number of successes), and p=0.005 (probability of success on a single trial) to find the probability. But without the actual prevalence rate for the light users, the answer would be speculative and not necessarily reflect the real situation.