A STATISTICAL METHOD FOR ESTIMATING HOW MANY PIANO TUNERS THERE ARE IN CHICAGO. The method used to estimate the number of rats in New York City is reminiscent of the answer to the question: How many piano tuners are there in Chicago? One answer is described in this wikipedia entry on Fermi problems. The answer suggested in the wikipedia entry comes from a series of ball park estimates.
” There are approximately 9,000,000 people living in Chicago.
On average, there are two persons in each household in Chicago.
Roughly one household in twenty has a piano that is tuned regularly.
Pianos that are tuned regularly are tuned on average about once per year.
It takes a piano tuner about two hours to tune a piano, including travel time.
Each piano tuner works eight hours in a day, five days in a week, and 50 weeks in a year.”