Question

To an order of magnitude, how many piano tuners are in New York City? The physicist Enrico Fermi was famous for asking questions like this on oral Ph.D. qualifying examinations. His own facility in making order of magnitude calculations is exemplified in Problem 45.48. (Explain what values you are using to make your estimate.)

Answer 1

Suppose the population of NY is 10,000,000. And there on average 3 people per HH (household)
=> 3.3 million HHs
...and 1 in 10 HHs has a piano
=> 330,000 pianos
...and on average a piano is tuned once a year
=> 330,000 tunings per year
=> ~6,000 tunings per week

Suppose a piano tuner works 5 days/week and can tune 5 pianos a day. That's 25 pianos/week.

Hence you'd need 6,000/25 = 240 tuners.

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Not really a Physics question, but sometimes in business interviews you're asked things like this. Being able to approximate is valuable.

Answer 2

10^2

Answer 3

Thanks man!