**Marketing Memetics**, by Michael Taylor

How many piano tuners are there in New York City? You may have been asked this interview question and been left scratching your head. Of course you aren’t expected to know the answer, the interviewer just wants to see how you think. These questions are called “Fermi Problems” — after the famous engineer who used them to estimate the strength of atomic blasts, the circumference of the Earth and the likelihood aliens exist.

It works like this: 1) break the problem down into smaller parts, 2) use common sense and make assumptions 3) calculate the answer by aggregating your guesses. For example we know roughly 8 million people live in NYC. Assume 5 people per family. Maybe 1 in 10 families own a piano. They need to be tuned once per year. If one piano tuner can do 4 per day, working 200 days per year, that’s 800 tunings each. Run the numbers and you get 200 piano tuners. Checking Yelp there are 24 companies listed: assuming each employs multiple people and all tuners aren’t listed, we arrived at a reasonable guess.

When you break a problem down into smaller parts, it becomes easier to estimate: simple enough to write on the back of a napkin. Even though each estimate might be off, aggregating lots of smaller errors cancels them out. You usually arrive at approximately the right answer, within an order of magnitude. That’s the power of decompositional reasoning: by breaking things into constituent parts and analyzing each part independently, you can draw powerful conclusions about the whole.

Name | Link | Type |
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7 Types of Reasoning: Definitions and Examples | Reference | |

Enrico Fermi | Reference | |

Fermi Problem | Reference | |

How Many Piano Tuners Are There In New York City? | Blog | |

Yelp Piano Tuners New York | Reference |