Entering, a salesperson's words

Part 1 Why Fermi Estimation Now?

01 The type of professional talent needed in the new era
02 The era of creating your own career
03 What can humans do in the AI ​​era?
04 Fermi Estimation: A Smarter Way of Thinking
05 Finding Answers to Questions Without Answers
06 People must be quantified in a humane manner.
07 Let's quantify ambiguous problems.
08 You must be able to think logically to solve problems.
09 The thought process is important in Fermi estimation.
10 Important assumptions, decompositions, and comparisons in the Fermi estimation
About the Fermi Column Estimation

Part 2 Home Training

11 How old is the person in charge of the first business meeting?
12 First, let's learn how to think as a family.
13 Let's convert intuition or subjectivity into numbers.
14 How to come up with a number that everyone agrees on?
15 Practice Problem Challenges to Help You Understand
Home Exercise: Converting Ambiguous State to Number
Home Practice Hints

Part 3 Decomposition Training

16 Let's break down the object into smaller pieces.
17 Let's divide the object using the four basic operations.
18 Let's create a decomposition brain that finds the cause of failure.
19 Let's make decomposition a habit.
Decomposition Exercise: Thinking, "What is that made of?"
Disassembly practice hints

Part 4 Comparative Training

20. You need a standard to compare.
21 You must be able to determine the comparison target.
22 Developing a sense of automatically quantifying comparison targets ①
23 Developing a sense of automatically quantifying comparison targets ②
24 What is the size of China's mask market?
Comparison Exercise: Identifying and Quantifying Comparison Objects
Comparison Practice Hints

Part 5 Comprehensive Training

Level 1
① How many people would it take to drink all the water from Lake Biwa in one day?
② If there was an open-air bath the size of Lake Biwa, how many people could fit in it?
③ How many trains run on the JR Yamanote Line at the same time?
Level 2
④ Sales must be made to major corporations in Tokyo.
How many people would it take to visit all the companies in three months?
⑤ What is the size of shoe sales in the Japanese running shoe market?
⑥ How many people do yoga in Japan?
Level 3
⑦ What is the daily sales of a curry restaurant in Tokyo?
⑧ How many managers are there in Japan?
⑨ How many stations are there in Japan?
Level 4
⑩ How many disposable masks are used per day in Japan?
⑪ How many Japanese people are on Instagram?
⑫ What is the annual rice consumption per Japanese person?
Level 5
⑬ How many domestic flights are currently flying over Japan?
⑭ How many people board domestic flights in Japan in a year?
⑮ How many traffic signals are there in Japan?
Data that is good to use as a column premise

Part 6: Mathematical Thinking for People Living in Uncertain Times

01 Mathematical thinking, not mathematics
02 What is mathematical thinking?
03 Understand the five concepts
04 Definition is to determine the scope of the object.
05 Change the definition and everything changes.
06 If you break it down into details, it starts to show
07 Let's do some decomposition training
08 You can also compare qualitative things.
Let's compare by converting to numbers 09
10 The object has a structure (texture).
Let's think about structuring examples 11.
12 Modeling is finding relationships between multiple objects.
13 Let's answer the questions using five concepts.

Going out

A powerful weapon required by the new era
An Introduction to Fermi Estimation: Developing Rational Thinking Skills

Google's recruitment interviews, a global company, are famous not only for their difficulty but also for their unique questions.
For example, questions like “How many piano tuners are there in the world?”
What's the purpose of asking questions like these, to which even interviewers can't pinpoint the exact answer? It's to assess your attitude toward the question and your critical thinking and logical thinking skills in finding the answer.
Most of the world's problems we face, whether in daily life or in business, often have no set answers.
In an age where many things are uncertain and machines are overwhelmingly superior at simple calculations, the real competitive edge that humans must possess is the ability to think intuitively and to define and solve problems on their own.
"10 Minutes of Logic Practice a Day for Better Decisions" suggests "Fermi Estimation" as a brain training method to improve such abilities.
Fermi estimation, which quickly utilizes limited information to form hypotheses and derives conclusions based on logical reasoning, will help us make better decisions in the numerous problems before us.


The Fermi estimate introduced in this book is a method of applying reasonable assumptions and logic to difficult-to-understand problems to produce an 'estimate' in a short period of time.
It can be said to be a mathematical process of logically inferring unclear numbers based on basic knowledge and limited data and obtaining approximate values ​​in a short period of time.
Fermi estimates allow us to make useful inferences from simple common sense in a short period of time.
This book is written in an easy-to-understand and fun way, especially for beginners who are new to Fermi estimation. It also includes examples, which will be of great help in solidifying the fundamentals of logic.
The book also provides an interesting and informative introduction to how easily Fermi estimation thinking can be applied in our daily lives, making it a valuable guide for those who wish to improve their mathematical thinking and logical thinking skills in their daily lives or work.
After mastering the Fermi estimation through this book, you will gain the ability to make the best decisions without panicking even in situations where there is no definitive answer.


Smart people think and speak like this!
3 Ways of Thinking That Make Difficult Problems Simple

Skillfully utilizing Fermi estimates can help you solve problems more calmly and wisely than you can now.
A systematic approach will improve your logical thinking, quick decision-making, abstract thinking, and even communication skills.
It is also useful in situations such as calculating the ripple effect that an event will have on the economy, selecting talent, or deciding which option is more advantageous.
Unlike simple memorization or calculation, Fermi estimation emphasizes the thought process that goes into arriving at an answer.
This book helps you express ambiguous things in numbers by learning three important thinking skills: 'assumption', 'decomposition', and 'comparison', and helping you solve real-world problems.
This is a training program that trains the brain to find solutions to difficult problems by effectively utilizing three different thinking methods.

There are three important ways of thinking about Fermi estimation:
'Assumption' is the step of converting information that is difficult to handle quantitatively, such as intuition, subjectivity, or an appropriate level that many people can agree on, into numbers.
Next is 'decomposition'.
It is about dividing the target into time zones or elements.
This step teaches you how to break the whole down into smaller parts so you can identify the problematic elements or key variables, and how to make this way of thinking a habit.
The third step explains ‘comparison’.
It is about learning how to create benchmarks, select comparison targets, and automatically quantify comparison targets.
To give an everyday example, you can compare your weight to the average weight of people of the same gender or age, or to your weight from a year ago, to estimate whether you are overweight.
By practicing how to build logic based on mathematical thinking through fun examples like this, you'll gain the ability to find the best solution to any problem without getting flustered.

Brain training recommended by consultants from major corporations and prestigious universities
The foundation of logical thinking that a capable member of society must possess

This book teaches you how to quantify data in a way that only humans, not machines, can do.
That is, it solves problems that do not have a set answer by quantifying information that is difficult to quantify.
For example, someone who knows how to use the Fermi estimate could give a numerical answer to the question, "Approximately how much profit did you contribute to the company in one year of work?"
There is a big difference in competitiveness between those who can answer their own value in numbers and those who cannot.
Fermi estimates are particularly helpful when working in business environments where data is scarce and uncertainty is high.


"10 Minutes of Logic Practice a Day for Better Decisions" is a book by a business mathematics expert who has taught logic to over 20,000 office workers. It guides you through a brain training method based on Fermi estimates that has been adopted by many companies.
Simply learning the Fermi estimation, the core content of this book, will improve your logical and intuitive skills, making you a smarter person and equipping you with more sophisticated problem-solving skills. This is very useful for office workers who want to seize opportunities for growth at work.
The author has lowered the barrier to entry by providing familiar and sufficient examples so that even beginners can easily get started.
In Part 1, we will define Fermi estimation, in Parts 2 through 4, we will learn the three most important elements for developing Fermi estimation skills, in Part 5, we will solve real problems by level, and in the final Part 6, we will talk about the power of mathematical thinking.
Fermi's method of reasoning, which helps people make optimal decisions in the face of uncertainty, will provide a practical guide for anyone seeking to improve their logical thinking.