> "how many golf balls can you get in a double decker bus" > My answer to the first was "I dont know and i'm not going to try and work it out because 1) i don

> "how many golf balls can you get in a double decker bus" > My answer to the first was "I dont know and i'm not going to try and work it out because 1) i dont have enough information and 2) its not relevant to this position. The genesis of these kind of questions is http://en.wikipedia.org/wiki/Fermi_problem http://en.wikipedia.org/wiki/Fermi_problem (checkout the classic "how many piano tuners"). Fermi approximation's purpose it to estimate without concrete data. In the end, if the numbers aren't right, you just need to replace the numbers, provided your method was correct. I am not contending its relevance(largely irrelevant). I am just pointing out the origin.