In my experience these "Fermi questions" aren't that useful, the primary thing they tell you is whether the person has previously been exposed to the concept of

In my experience these "Fermi questions" aren't that useful, the primary thing they tell you is whether the person has previously been exposed to the concept of "Fermi questions" or not. I guess if the person being interviewed is 30+ and working in software development and hasn't been exposed to Fermi questions then maybe that's a red flag, but other than that I've seen no indication that answering these types of questions well correlates to real world performance.