Part 1.
In-depth exploration of principles

Lesson 1: Angle of the clock hand
Angle formed by two clock hands
Sum of the angles of three plane figures
4-way vertical angle
The five inner and outer cabinets
6-angled right triangle
Lesson 7: Rotating Complex Shapes
Making a simple 8-round rotation 1
Making a simple 9-turn loop 2
Lesson 10: Moving Shapes
Lesson 11: Finding the number in a sequence

Part 2.
Explanation of conditions

12 folded shapes
Lesson 13 Two shapes of the same size and shape
Lesson 14: The Relationship Between Multiplication and Division
Finding the Quotient and Remainder in Equation 15
When the quotient and divisor are the same in the round of 16
Lesson 17: Intervals and Numbers 1
18th round interval and number 2
Lesson 19: A Clock Reflected in a Mirror
Lesson 20: Finding the Hidden Rules

If you study elementary mathematics in depth, you will encounter the following difficulties.
First, it is a problem that contains logic that is difficult to solve using only the concepts and principles of the subject.
Second, for advanced problems, it is difficult to practice similar problems.

This book aims to teach students who want to tackle difficult problems and develop skills beyond the concepts of the subject, including the required "principles and concepts," "conditions and rules," "special calculation methods," and "problem-solving techniques," through video lectures.
While typical math textbooks are structured to challenge students with a list of problems, this book selects 40 concepts and problem-solving methods that students must know after learning the basics of the subject each semester, and encourages students to learn them on their own, sometimes through questions, sometimes through video lectures, and practice with confirmation problems.

If you're struggling with word problems, you'll often hear advice to read a lot.
Is the difficulty with math word problems really a problem of reading comprehension? While it may have a slight impact on early elementary school students, the reason they struggle with word problems is because, even if they read the problem carefully, they don't understand the key conditions or don't know where to start and how to solve it.

The way to do well in word problems is to learn various conditions and problem-solving methods logically.
That is, by increasing your mathematical background knowledge, you must acquire the skills to interpret the mathematical meaning hidden in sentences and solve problems easily and logically.
Solving a lot of sentence-based problems doesn't make you better.
The essence of a word problem is not the sentence itself, but the difficult mathematical conditions.

Warm!! I hope that elementary math, which can be solved by following along, will be a blessing to students who have difficulty with advanced learning.