Sophie wrote:

> I got a slightly different answer for Puzzle 57 and was wondering what you all think!

> Puzzle 57. My interpretation of the problem was that you don't need to do every task, you only need to visit each preceding state. By skirting around task E, you can do this in 7 months no matter how long task E takes. Thus, task E can take an arbitrary amount of time without changing the answer to Puzzle 56.

Very good point! This is a perfectly self-consistent viewpoint. But now that I think about it, I'm pretty sure that people who use PERT charts usually say you must accomplish every task (=arrow) pointing to a given state (=node) before you can go ahead and do further tasks pointing out of that state.

So, my description of the problem was inaccurate, at least for PERT charts as ordinarily used. I've fixed my lecture, and explained the change in [comment 2](

One annoying thing about the Wikipedia article on PERT charts is that they don't start by clearly stating the rules of the game.