Source: University of Western Ontario
Published: November 2018
Fermi Questions
Circulated: May 11, 2020
A “Fermi question” is a question in physics or mathematics which seeks a fast, rough estimate which is either difficult or impossible to measure. It is designed to teach approximation, also known as back-of-the-envelope calculations.
Example question
What is the circumference of the Earth?
1. How many time zones do you pass through flying from New York to Los Angeles?
Answer: 3
2. How many miles is it, about, over that same distance?
Answer: About 3,000 (4,800 km).
3. How many miles per time zone, on average?
Answer: About 1,000 (1,600 km).
4. How many time zones must there be around the world?
Answer: 24 because there are 24 hours in a day.
5. How many miles around the world?
Answer: 24 time zones x 1,000 miles per time zone = 24,000 miles (38,000 km)
Yes, it is about 24,000 miles around the world. The actual distance is 24,901 miles (40,075 km).