This is a Fermi estimation problem and it's easy.
You have probably heard of similar questions (Google asked them in interviews!) and there is a simple lifehack to solve this by findind an answer within an order of magnitude (10^1):
How many people live in Berlin: 100k, 1M or 10M?
Without googling I would estimate there live more than 100k and less than 10M, so I'll go with 1M.
How many people have pianos in Berlin: 1 out of 10 has one, 1/100 or 1/1000?
Let's go for the middle answer (1/100) since we account for children as well. This means we are estimating 1M people x 0,01 piano distribution = 10k pianos in Berlin
How many pianos can be tuned by one tuner in a year: 10, 100, 1000?
Again, let's go for the middle answer and estimate 100 pianos
Result: 10k pianos / 100 pianos tuned = 100 piano tuners.
I checked Google and Yellow Pages (for real!) and there are around 60 piano tuners in the Berlin metro area.
I would say that's a pretty accurate estimation for the little data we had available!
Startups need to solve problems in constant uncertainty. Estimating an outcome with little data helps navigating the darkness.
I first published this article on LinkedIn