But regularly solving problems outside of your expertise is a necessary job duty in pretty much any software job. (If I were conducting the interview, I might

But regularly solving problems outside of your expertise is a necessary job duty in pretty much any software job. (If I were conducting the interview, I might explicitly explain that I'm going to ask them a few questions with the goal of seeing how they perform when they reach the limits of their crystallized knowledge and have to problem-solve from first principles/common sense — but I would still do it.)