Interview techniques: the rise of Fermi questioning

When was the last time someone asked you a tricky question? 

Do you ever feel you’re being asked something just to test your reaction?

In interview situations this is happening increasingly often with the rise of a particularly interesting interview trend – Fermi questioning.

Fermi itself isn’t a new concept.  Enrico Fermi was a Nobel Prize winning physicist with an impressive knack for solving seemingly unsolvable or overwhelming estimation problems with impressive speed and accuracy (the kind of guy who works on the creation of the first atomic bomb…but enough about him). Fermi questions are the new ‘fun’ questions’ that seasoned interviewers like to throw in to test how your mind works and how you go about problem solving but also, they instate power.

The large, ‘trendy’ corporates like Google and Microsoft are notorious for asking these questions but recently we have noticed other companies adopting this technique to the extent that Fermi questioning is now becoming a regular fixture in interviews.  As a result, this had led to a rise in candidates baulking at their interviewers in complete surprise and shock when asked:

“How many piano tuners are there in the city of London?

We need an answer, and we need it in the next sixty seconds. Oh, and no using Google, either.”

How would you react to this type of question? Would you give up?  Many people do.  Indeed, a lot of people don't even know how to begin to answer a question like that.

Ultimately the answer itself is somewhat irrelevant.  The thing that will set you apart from other candidates is how you choose to think about the question or problem, and often this can be as complex, or as simple, as you want to make it.

For example, in response to the question above, you could just pick a number you deem to be reasonably accurate or you could start with a number you’re fairly certain about and explain your reasons why. For example, there are roughly 8 million people in London – the average number of households that have a piano is 1 in 50, they all get them tuned once a year, a tuner can do 5 tunings a day, he/she works 230 days a year. On this basis there are approximately 140 piano tuners in London.

A quick Google search (after the interview of course) shows that amount of listings in the Yellow pages are 94 – considering some may be multiple piano tuners I’d say that my estimations are fairly accurate.

Exploring these lower-level Fermi problems is one way to highlight your ability to think in creative or abstract ways, but it can also indicate that you don't know when to stop overanalysing and just answer the question.

Have you ever been to an interview where Fermi questioning has been used?
What questions were you asked?