I'm with Gary. We all get faced with unexpected situations from time to time and the interesting bit here is NOT the answer, but how the candidate (or me) thinks in trying to get to a solution...

How many hair stylists are there in Munich?

Hmm lets say the population of Munich is 1million (I'm sure it isn't)

Lets say on average people get their hair done every four weeks. (I mean who really cares?)

So that's 250,000 cuts/month

Lets say each cut takes half an hour (you can tell it's a guy doing this...)

And so on...

It is also JUST as revealing if the candidate sits there and say's "I have no idea."