Fermi Problem: Brainteaser Interview Questions

I am sure you all heard one of these famous interview questions:

1. How many gas stations are there in the US?
2. How many pennies can you put in Empire States Building?
3. How many piano tuners are there in New York?
4. How many dentists are there in the Bay Area?

All these interview questions are called "Fermi problems" or "Fermi questions". It simply is an estimation problem about capturing 2 things:

1. Being able to explain your assumptions
2. And using these assumptions performing an approximation

Let's take a look at the 4th question: How many dentists are there in the Bay Area? We can solve it by:

1. There are approximately 10 million people in Bay Area
2. Let's assume on average 2 in 5 people go to dentist in Bay Area
3. On average people go to dentist twice a year
4. A dentist with his/her helpers can see 80 patients a week (1/2 hour per patient)
5. On average a dentist takes 2 weeks of vacation per year (They work 50 weeks per year)
6. Bay Area has sufficient dentists

Let's say our assumptions and approximations above are correct, then there are 4 million people go to dentist, which results in 4 million visits per year. A dentist can handle 4000 visits per year = 80 visits x 50 weeks. Therefore the Bay Area has approximately one thousand dentists = 4 million / 4 thousand. 

If you have a lot of time on your hands you can try to solve the following problems with Fermi estimation:

http://www.physics.umd.edu/perg/fermi/fermi.htm

 

 

Comments

[interview questions]

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