[Doctor Stochastic]

The original math is correct under the stated assumptions.

First that condom failure is "random" in that one doesn't get a bad batch of condoms or a good batch.

Second, that the partners are chosen "randomly" (independently and identically distributed); a succession of one-night stands would be an example. Things would be different with a single partner who was known to be HIV positive.

The math is correct. The actual probabilities would have to be obtained through observation.

I didn't really understand the objection; it seemed to be poorly written.

[monkey]

I didn't really understand the objection; it seemed to be poorly written.

That is being charitable. It's sad to think that the person must have taken some math/stats.

[general_re]

The original math is correct under the stated assumptions.

I suspected as much, but it's always nice to have some backup ;)