Part 1.
In-depth exploration of principles

Lesson 1: Decomposition of Multiplication
2nd lecture remainder and shortage 1
3rd class remainder and lack 2
Check formula for 4-term division
Lesson 5: The nature of remainders
The quotient and remainder of the value of the 6th equation
Lesson 7: Proper Fractions and Mixed Numbers 1
Lesson 8: Proper Fractions and Mixed Numbers 2
9th lecture □ as many as fractions 1
2 as many as the fraction of □ in the 10th class

Part 2.
Explanation of conditions

Lesson 11: The Meaning of 'At Least'
12-point gap and interval
13. Length of overlapping tape
14. The distance between two people
Lesson 15: Problems using tea
Age issue in the round of 16
Lesson 17: Calculating Parallax
Diameter and Radius of a Circle, Lesson 18
Lesson 19: Perimeter of Circles and Shapes
A shape created by connecting the centers of 20 circles

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.