Fermi method: learning how to measure the unknown

What is the method

According to Enrico Fermi, the famous physicist and master speculation, every person is capable for 60 seconds to evaluate anything. Find the answer may be in the most unusual question. For example, what is the size of the market razors in China or how many balls will fill the school bus for the course.

The essence of his method of solving such problems lies in the fact that for a very short time to hold fast approximate calculations, without having any precise data. His method of calculating involves not conduct new measurements and work with what is already known about the problem.

The method is based on the belief that all knowledgeWe possess, are interrelated and in fact there is no issue on which we did not do any information. Therefore, having just a few facts and having the ability to think logically, you can find the answer to any, even the seemingly unsolvable problem completely.

How it works in practice

How many piano tuners in Chicago - the most famous question that Fermi often asked my students.

At first it seems that it is impossible to answer. But Fermi method and is not intended to obtain an accurate result. The most that can and need to do - to give a reasonable estimate based on sound assumptions. That is, specify the approximate value or range of values, denoting thus possible errors and deviations.

Here is the solution of the problem stated above.

• We estimate the population of Chicago: it is about 2.7 million people.
• We figure out how many families live in the city. To do this, roughly assume that every family of 2-3 people. Then divide the entire population on an average of 2.5, and in the end we get about a million families.
• How do I know how many of them have a piano? This is the most complex figures identify them accurately without research impossible. Therefore, it remains only to assume, guided by common sense and experience. Take five percent of all households - it will be about 50,000.
• Assume that the average piano tuned once a year - it turns out that for the year in Chicago need to cater for 50 000 tools.
• How many days per year worked tuner? 365 days subtract 52 Saturdays and 52 Sundays and holidays a few days. It comes out to about 250 days.
• The day may come customizer to four families - this is also the approximate number. It depends on the time spent on the road, and in each case. But it tells us that in the year one person can produce about 1000 settings: we multiplied the four instruments per day for 250 working days.
• Dividing 50,000 options per year in 1000 setting produced this year one person gets 50 tuners in Chicago.

It is clear that in the end we have an approximate number. But it narrows the range of values ​​within which to work with. Fermi opinion, an amount that seems most uncertain (eg, how many families can stand upright piano at home), you need to measure in the first place, to get more accurate data.

Single algorithm for solving all the problems of the Fermi does not exist, but there are a few rules to follow:

• Even if it seems that you have absolutely no clue about the subject matter, believe that you just need to find its own approach. You probably have information that one way or another will bring you closer to the correct answer.
• Involve your existing knowledge from various fields and regions to find a proprietary algorithm solutions.
• Spend all the necessary evaluations and preliminary calculations.
• What are the concrete answer, tell us what deviations from the actual outcome may be and why.
• Do not resort to the help of third-party sources.
• Do not be afraid slip up.

Why do we need a method

Fermi method is applicable in cases when you need to quickly give an approximate answer and only then decide further calculations to find the exact data whether it is advisable to carry out.

It can be used to refute the information, make a decision quickly, to understand in which direction to go and what kind of data is not enough.

The main thing is taught by Fermi method - better get approximate results than nothing at all.

For example, a businessman wants to bring to market a new product, but doubted whether it demand. Conduct costly research? But what if the money spent on it will go to waste, and the goods would be no use to anyone? As a result, people may hesitate long, wasting time, or even to abandon their ideas, fear of the unknown.

Using the Fermi method, the entrepreneur can independently assess, for example, changes in the purchasing power, popular trends, conduct quick analysis of the population's needs and rough calculations.

On the basis of approximate results he already can decide whether or not to invest in further research. And in the end, even a small reduction in uncertainty can bring us millions or save them.

The ability to use the method can also be useful to those people who do not have to make difficult decisions related to the high costs and risks.

Fermi questions may arise during the interview in a large company.

specialists recruitment use problems solved by Fermi, in order to learn how the applicant will be able to apply their knowledge in practice. At the same time for them is not so important to hear the correct answer as to follow the progress of thought.

And at the Fermi questions it has an important advantage: they can be very easy to invent in different variations, and to know if this the right decision is not necessary.

For example:

• How many pieces of popcorn you need to fill a room?
• What is the surface area of ​​the body of all people on Earth?
• How to write pages of text to read it out loud for one hour?
• Estimate the number of taxis in your city.
• How many books are printed annually in the world?

These tasks help to objectively evaluate the real-world knowledge. So you have to stretch the brain, and use logical thinking.