[mathattack]

The answers may get better, but don't you want to find out which candidates are more likely to bluff when they're wrong? The point of the interview isn't for candidates to give you answers that are as correct as possible. If this were the case, you'd mail them a list of questions, and ask them to get back to you in a week. One goal of interviews is to find out how people behave when they don't know. This is why I try to take people to the end of their knowledge, no matter where that end is.