by giladedelman Tue Jan 18, 2011 10:37 pm
Thanks for posting!
Without a doubt, this question is going to take longer than the others. This is usually true of questions that ask us to add or substitute a constraint. My approach here was to go back to the constraints and build a new diagram from scratch, keeping in mind that lecture 3 can now be M, N, or S. Since it's no longer the case that M and N have to go in 3 and 4 (since 3 could be S, and 4 is either M or N), we end up knowing a lot less about what goes where. That's okay, though. We should be confident that we know enough to evaluate the answer choices.
(A), (C), (D), and (E) all could be true because if we can place S third, it's okay to place M and N elsewhere.
(B) cannot be true because if M is second and N is third, that leaves no options for the fourth lecture.
So, I guess the takeaway here is, it's fine to spend some extra time on a question like this. Don't be hesitant about building up a new diagram that incorporates the new constraint; once you do, it shouldn't be too hard to move quickly through the answer choices.
Does that answer your question?