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

- How many gas stations are there in the US?
- How many pennies can you put in Empire States Building?
- How many piano tuners are there in New York?
- 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:

- Being able to explain your assumptions
- 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:

- There are approximately 10 million people in Bay Area
- Let's assume on average 2 in 5 people go to dentist in Bay Area
- On average people go to dentist twice a year
- A dentist with his/her helpers can see 80 patients a week (1/2 hour per patient)
- On average a dentist takes 2 weeks of vacation per year (They work 50 weeks per year)
- 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 8 million visits per year. A dentist can handle 4000 visits per year = 80 visits x 50 weeks. Therefore the Bay Area has approximately 2 thousand dentists = 8 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

When you go to a job interview, you expect them to ask you questions, but more often than not, they will turn the tables on you and finish the interview by asking if you have any questions you’d like to ask them. What they’re looking for here is to see whether or not you care enough about the job to get clarification on the position and company you’re joining. Impress your interviewer by asking a couple of our sample concluding job interview questions.

Posted by: interview questions | January 11, 2012 at 05:37 AM

Nice post.

Please visit my post on Fermi Questions – ‘How many people all over the world take their supper at sharp 22:00 IST hours during summer season?’at http://technogeny.blogspot.in/2012/03/how-many-people-all-over-world-take.html

You can also take the help of the technique to calculate the number at a different time of the day.

Please share the post if you have liked it.

Posted by: Techno Geny | April 04, 2012 at 10:10 PM