How much should we be trusting our own intuition when we read these? For this one, I found I was able to use my intuition to get to the right answer quicker than following these steps. That said, following these steps makes me make sure that I am not confusing the necessary and sufficient, which I can sometimes do! I guess my question is, how do you know when you can trust yourself to take the training wheels off? Is that something we can do via blind review (check answers using this formula) or is having the training wheels faster every time?

The contrapositive argument for the Melissa one is confusing. Is saying less not confusing negation with opposition? Would it not be "not more than 5 minutes late" rather than less? I mean, I know in effect that is less, so I guess negation and opposition can indeed be the same?