You are correct, there are indeed 2 approaches, but I wouldn't call them "European" or "American". It's just a different way of doing it:
First approach: You calculate the network diagram starting on day 0
Second approach: You calculate the network diagram starting on day 1
I personally use the second approach, because when my sponsor tells me, that my project starts on the first day of September, then that is September 1 and not September 0. This is also the way that all modern scheduling tools seem to work. You schedule your project based on a calendar start date and not "on day 0".
That is why there is a slight difference between the calculations (you have to add/subtract 1 from the results in the 2nd approach). However, don't worry about this for the exam too much. The way that the question is formulated you should be able to identify how to go about this. Also: I understand that in most cases when you have to calculate this, it is the end result that is important and not how you got there.
Until Next Time,
Cornelius Fichtner, PMP, CSM
President, OSP International LLC
Moderators: Yolanda Mabutas, Ahmed Amin, Scott Gillard, Mary Kathrine Padua, ERIC BARTLETT, Gail Freedman, Kevin Nason, Steven Mudrinich, PMP, Mark Wuenscher, PMP, John Wolverton, Tracy Shagnea, PMP, Jada Garrett
This interview with Simona Fallavollita (LinkedIn Profile) was recorded at the magnificient Project Management Institute (PMI)® Global Conference 2017 in Chicago, Illinois. We discuss the how, what, why and when of the changes that are coming to the PMP exam.