Your last example is not applicable. The question is comparable to a gun with infinitely many chambers, each with a 1/80 chance of containing a bullet: How man

Your last example is not applicable. The question is comparable to a gun with infinitely many chambers, each with a 1/80 chance of containing a bullet: How many times on average can you point it at your head and pull the trigger? The differences are that you have no guarantee that the first 80 chambers will contain exactly 1 bullet, that more than one chamber can contain a bullet, and that you can pull the trigger more than 80 times.