The classic “Fermi Question” (used in job interviews and the like) is to ask, “How many piano tuners are there in Chicago?”
If you answer, “I don’t know!”, then you fail. Of course you don’t know, but you can make some quick assumptions and calculate an estimate. The idea is to test if someone can think clearly. Do they make their assumptions clear? Is their reasoning logical? Do they clarify that it’s an estimate, but that it’s probably in the right ballpark?
This morning, it occurred to me that there’s now another way to estimate the number of piano tuners in Chicago: Ask Google Maps!
It even plots them on a map and gives details like name and phone number.
Of course, the money number is…
So there you have it: there are approximately 113 piano tuners in Chicago. That’s probably a low estimate because even Google won’t know them all. It’s interesting how close that number is to the estimate derived in the Wikipedia article on the Fermi Question: 125.
Troy McConaghy 
Hello,A datapoint to contribute to your blog post: I am a piano tuner, and I live in Chicago. Therefore there are >=1 piano tuners in Chicago. I’m not sure if there are 100. My dear friend Allen Schwamm passed away in 2005, so scratch C. Linconwood is not really Chicago, so I wouldn’t count H and I.Joe
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