3 Fermi problems
The Italian scientist Enrico Fermi (1901–1954) was famous for doing rough calculations based on very little information and getting surprisingly good estimates.
A famous example of his was: ‘How many piano tuners are there in Chicago?’
To tackle this, Fermi made reasonable assumptions about:
- what proportion of households have a piano
- how many times a year a piano will be tuned
- how long it takes a piano tuner to tune a piano
- how many hours a piano tuner works per year.
Combining these estimates with the number of people in Chicago, he arrived at a figure of 225. For comparison, according to WolframAlpha, the actual number in 2009 was 290. Taken with the fact that the population of Chicago has shrunk since Fermi's day, this means his estimate was a bit low. But still it is a remarkably good 'ball park' figure, given how little information he began with.