Your professor gave you such a question?
The probability that a person have HIV is:
(Problem is, we do not know the male/female population. I will assume it is equal then what I said is true).
I will assume when it is protected the probability is zero. Thus, the harlot did it twice with two different men. The 18 make no difference it was protected.
The probability she did contract HIV is (assume unprotected leads to HIV):
Thus the probability the harlot is safe is about 94%.
Even here we have a problem, as we don't know the infection prob. per
encounter, but it is definitly less than 1
There are lots of other things we don't know which make this an impossibleThus the probability the harlot is safe is about 94%.
sum, we need to know the hetro infected population, and ...
Also it does not look like homework to me...
All we can say is the use of a condom should make the transmission via
the obvious route unlikley, but there are other transmission mechanisms
about which very little is known.
RonL
RonL