It was a trick question...critical path should not have any slack
^^That's not exactly true. Tasks on the critical path refer to the tasks with the least amount of slack, or better put, tasks that if not completed first will adversely affect the end date of the project. I've seen some PM's consider tasks with <5 days of slack as their determining factor, others go as high as 10 days. Either way, it wasn't a trick question, the interviewer just wanted to see if you understood what the Critical Path was.
Side note: Are you kidding me? This was the typical types of 'behavioral' interview questions they threw at me. Fortunately, many large corporations handle interviews this way, so I came somewhat prepared Answer: I described a situation in my senior design project in how we had trouble with a certain individual not meeting deadlines. I described how the individual was confronted and how I positively encouraged a plan to help with the team's success. I got the job; I guess they liked my response (and a true story!).
This is inappropriate question, in my opinion, and the answer should not affect the employer's decision making of hiring. This kind of questions stands on the same level as religion and race for a lot of people.