A difficult interview question

In my role as system architect I get to interview the people for positions on my team. Most of my colleagues will ask the pure knowledge questions like "How would you implement an abstract class of vehicle given that you need subclasses of car and bus?" This kind of question shows that you understand OO concepts or you don't. Some of my questions are like this but I utilize some that are more vague. The one question that I always use will be

"Given a hypothetical project with 5 sub tasks, 3 of which you have done before and know how to do, and the last 2 are new techniques you have never done before - Given a hard deadline tell me in what order do you do the tasks?"

Most inexperienced people will say "I will complete the easy tasks and then complete the hard tasks." Some people with experience will say the opposite. Either answer is correct, but the real question is next - "Why". Many candidates have a difficult time clearly explaining why. My preferred answer places the unknown tasks ahead of the known tasks for one simple reason. It eliminates risk from the project. If you perform the 3 known tasks and then get to the unknown tasks and discover that they cannot be completed, then you have failed in completing the project and expended the energy to do the 3 known tasks. If you attempt the 2 unknown tasks first then you might discover in the early phases that the project cannot be completed before you attempt the 3 known tasks.

Net take away: Always take the path to eliminate risk from your project as soon as possible.