■ Preface · 4
■ To the 4th revised edition · 10
■ Concept Connection Elementary Mathematics Dictionary User's Manual · 20

1st Grade Math Dictionary

Numbers and Operations
Are there different ways to count numbers up to 9? · 30
Why is the number '8', up to 9, sometimes read as 'pal' and sometimes as 'yeotd'? · 34
Why do we learn addition and subtraction and what not to know? · 38
If there's "all" in an addition or subtraction problem, shouldn't you just add all the numbers? · 42
Addition and Subtraction: Isn't 5 - 3 = 3? · 46
Addition and Subtraction How do you convert an addition expression into a subtraction expression? · 50
The number 'forty-six' up to 100 can be written as '406', right? · 54
If you can tell which number is greater by just looking at the numbers up to 100, why do you have to count them? · 58

Change and Relationships
Finding a Pattern It says to find repeating patterns, but I really don't know what is repeating.
· 62
Find the Rule I can't solve the problem of finding the rule and having to color the next color.
· 66

Shapes and Measurements
Are there only various shapes? · 70
We all know that various shapes like □, △, and ○ are squares, triangles, and circles, but why aren't they shown in textbooks? · 74
Compare "tall building" and "tall building." Which is correct? · 78
When I look at the clock, I get confused between the hour and minute hands.
· 82
When I look at the clock, I keep reading 1:30 as 1:06.
· 86

2nd grade math dictionary

Numbers and Operations
How does the 4 in the three-digit number 427 (400) come to 400? · 96
Addition and Subtraction 9 - When calculating 5 + 4, I calculated the addition first and then did the subtraction.
· 100
I get confused when addition and subtraction problems appear horizontally.
· 104
Addition and Subtraction I don't know where to use the number carried over in addition.
· 108
I solved the addition and subtraction problem and got the answer, but why does it keep asking me to try another way? · 112
Addition and Subtraction: Why is the answer box in the middle of the equation? · 116
Isn't the one with the four digits larger the bigger number? · 120
Multiplication Tables: Are the multiplication tables multiplication? · 124

Change and Relationships
Is it also a rule that the number of rules to find is decreasing? · 128
I can't explain the rules of the array table for finding rules.
· 132
Finding the Rules What are the rules for wrapping paper with complex patterns? · 136
Find the Rule: If you flip or rotate it, doesn't it become a different shape? · 140
I listened to the explanation of finding the rule and built it, but why is the shape different? · 144

Shapes and Measurements
Various shapes, are these shapes also triangles? · 148
Why learn to measure with your hands or feet when you have a ruler to measure length? · 152
How do I measure length as 10cm or 10cm? · 156
How is 1 meter 20 cm equal to 120 cm? · 160
Do you really need to know how to read a clock with hour and minute hands? · 164
Time and Time What time is it now? · 168
Is 1:00 AM AM or PM? · 172
Why isn't the last day of February the same as the last day of the month? · 176

Data and possibilities
How do I categorize? · 180
I can't find the classification criteria in Classify.
· 184

3rd Grade Math Dictionary

Numbers and Operations
It's confusing when you do addition and subtraction twice.
· 194
How does the division '8 - 2 - 2 - 2 - 2 = 0' equal '8 ÷ 2 = 4'? · 198
Division I can't express the division situation in a picture.
· 202
Division Can't Divide Anymore! · 206
If it's one of two fractions and one decimal (1), then it's 210?
Between a fraction and a decimal, isn't the one with the larger denominator the larger number? · 214
Fractions and Decimals What are decimals? · 218
How much is the fraction 6? · 222
If a fraction is a false fraction, does that mean it's not a fraction? · 226

Shapes and Measurements
If you draw a plane figure straight, aren't they all straight lines? · 230
Are the plane figures ㄱㄴㄷ, ㄷㄴㄱ, and ㄴㄱㄷ all the same? · 234
In a plane figure or a tilted figure, you can't find a right angle.
· 238
All quadrilaterals with right angles are rectangles, right? · 242
Circles, triangles, and squares are drawn using a ruler, but how do you draw a circle? · 246
Doesn't a circle have a diameter of 1? · 250
Does it make sense that my height is 140 cm but my shoes are 210 cm? · 254
I'm curious about the relationship between length and time, km and mm.
· 258
How do I calculate the distance and time between 2 km 200 m and 1 km 800 m? · 262
Isn't 1000g heavier than 1kg? · 266
What exactly are load and weight loads? · 270
How do you calculate the volume and weight of 3L (600mL) and 5L (700mL)? · 274

Data and possibilities
Is it necessary to include a picture in a data organization graph? · 278

4th Grade Math Dictionary

Numbers and Operations
The big number 24 is twenty-four, 204 is twenty-four... What's wrong? · 288
How do you read the large number 8326801023603167? · 292
Large numbers like 1,000 or 10,000 are separated by commas.
Do I really have to take a picture? · 296
If a number is big, isn't it a big number? · 300
To calculate 400 × 500, multiply 4 by 5 and add 4 zeros, right? · 304
As the number of multiplications and divisions increases, I keep getting confused when doing multiplication.
· 308
Multiplication and Division: Why do we subtract when it's division? · 312
Adding and Subtracting Fractions Why do we add only the numerators and not the denominators when adding fractions? · 316
Addition and Subtraction of Fractions: Can't you just add mixed numbers without converting them to improper fractions? · 320
Sometimes you are asked to solve addition and subtraction problems with fractions in two ways.
Why do I have to solve it in two ways when I can find the answer? · 324
Addition and Subtraction of Decimals I'm not sure where to put the decimal point when adding decimals.
· 328
Addition and subtraction of decimals: Why do we need to find the number of 0.1s when calculating 1.5 - 0.7? · 332
Addition and subtraction of decimals. Just like with natural numbers, you just need to match the last digit, right? · 336

Change and Relationships
In a rule-finding problem, you can draw the next picture, but it is difficult to express it in numbers.
· 340

Shapes and Measurements
Every time I measure an angle with a protractor, the angle is different. · 344
The angle I measured was 45 degrees, but it turned out to be 135 degrees? · 348
How do you add and subtract angles? · 352
I don't know what an acute angle is, a right angle is, or an obtuse angle is.
· 356
Why is it called an obtuse triangle if two of its angles are acute? · 360
They ask me to flip the moving figure of a plane figure, but when I flip it, there is nothing there.
· 364
An isosceles triangle is a triangle with two sides of equal length, but how can two angles also be of equal size? · 368
What's the difference between right angles, vertical lines, and perpendicular lines in a square? · 372
I measured the distance between parallel lines in a square, but the result is different each time I measure it.
· 372
How is a square parallelogram a trapezoid? · 380
Is a square a rhombus? · 384
I think that if we use regular polygons, we can cover the plane without any gaps.
· 388

Data and possibilities
Why draw a bar graph when a bar graph would suffice? · 392
What and how are the horizontal and vertical bars of a bar graph displayed? · 396
Can you predict the future using a line graph? · 400
Line Graphs: Is there anything that needs to be represented specifically as a line graph? · 404
Why is there a broken line graph (wavy line)? · 408

5th Grade Math Dictionary

Numbers and Operations
Mixed Calculations of Natural Numbers: 8 - 10 ÷ 5? The problem seems odd. · 418
Since you said that you calculate the mixed multiplication and division of natural numbers first, should we calculate the multiplication first? · 422
Divisors and Multiples: Is 5 a multiple of 5? · 426
Factors and Multiples: Factors are numbers that divide evenly, so why do we multiply them to find them? · 430
The greatest common divisor is greater than the least common multiple, right? · 434
What happens if you multiply the numerator and denominator of a fraction by 0? · 438
I don't know how to express it in reduced form and common fraction.
· 442
If you multiply the denominators of a fraction and a common fraction, you get a common fraction, right? · 446
How do I know the larger number between the common denominator and the common fraction? · 450
How do you add and subtract fractions when the denominators are different? · 454

Change and Relationships
I can solve the problem by looking at the rule and corresponding picture, but it is difficult to express it as a formula.
· 458

Shapes and Measurements
Congruence and Symmetry: Are flipped and overlaid also congruent? · 462
If you know the measures of the three congruent and symmetrical angles, can't anyone draw the same triangle? · 466
What are congruent and symmetrical lines? · 470
Congruent and Symmetric Figures: It's only natural that symmetrical figures have a symmetry axis! · 474
What's the difference between a rectangular solid and a cube? · 478
The rectangular solids have different developments, but they are the same rectangular solid? · 482
Drawing a rectangular solid is difficult · 486
I'm asked to find the perimeter and area of ​​a polygon and the perimeter of a triangle. What is the perimeter? · 490
Which polygon has a larger perimeter or area? · 494
How do I find the area of ​​a polygon when its perimeter, area, and height are tilted? · 498
There are many different types of triangles, so how do you find the area of ​​all triangles using (base) × (height) ÷ 2? · 502
The perimeter and area of ​​a polygon Since a rhombus is also a parallelogram, finding the area of ​​a rhombus is the same as finding the area of ​​a parallelogram, right? · 506
Why is finding the perimeter and area of ​​a polygon and the area of ​​a trapezoid so complicated? · 510

Data and possibilities
When calculating the mean and likelihood mean, shouldn't you choose the middle value among the given data? · 514
What do we learn from the average and the probability? · 518

6th Grade Math Dictionary

Numbers and Operations
How does ÷ become 6 ÷ 2? What about the denominator? · 528
Division of Fractions: Why is division rewritten as multiplication? · 532
Division of Decimals: Why do we move the decimal point when dividing decimals? · 536
When moving the decimal point in division of decimals, why doesn't the decimal point of the remainder move? · 540

Change and Relationships
Are the ratios 1:2 and 2:4 the same? · 544
Proportional Formula and Proportional Distribution When mixing sugar and water in a 1:3 ratio, how much water should be added if the sugar is 50g? · 548

Shapes and Measurements
The base of a prism or pyramid is the surface at the bottom, right? · 552
I'm trying to measure the height of a prism and a pyramid. Can I just measure the length of the side edges? · 556
Is there an easy way to count the number of spaces and three-dimensional stacking blocks? · 560
How do you represent the shape of stacked wooden blocks in space and volume? · 564
Cylinders, cones, and spheres I'm confused about cylinders and cones.
· 568
How do you calculate the volume and surface area of ​​a rectangular solid and how much wrapping paper is needed to pack a box? · 572
How do you find the volume and surface area of ​​a rectangular solid? · 576
What's the difference between the area of ​​a circle, circumference, and pi? · 580
Area of ​​a Circle: A circle has no length or width, so how do you find its area? · 584

Data and possibilities
How do I represent quantities shown in various graphs on a bar graph? · 588
How do I draw tick marks on various graphs? · 592

■ 2022 Revised Elementary Mathematics Curriculum List · 596
■ Elementary, Middle, and High School Math Concept Connection Map · 600
■ Browse by Topic · 602

1.
The undisputed #1 in the math dictionary field, 『Concept Connection Elementary Math Dictionary』,
A completely revised edition reflecting the new curriculum for all grades has been published!

The "Concept Connection Elementary Mathematics Dictionary" has been completely revised to reflect the new curriculum that will be applied to elementary schools starting in 2024.
What would have been different?

① As always, the concept of mathematics does not change just because the curriculum is revised.
However, some movements and changes in terminology have been revised to fit the new curriculum.
As the new curriculum will be applied to 1st and 2nd grade textbooks in the 2024 school year, 3rd and 4th grade textbooks in the 2025 school year, and 5th and 6th grade textbooks in the 2026 school year, the 『Concept Connection Elementary Mathematics Dictionary』 has also been revised.

② The [Elementary, Middle, and High School Math Concept Connection Map], which connects 12 years of math concepts from elementary to high school math, has been completely revised to match the new curriculum.
Strengthening connections, which are a part of the mathematical process, has the effect of compressing the overall volume of mathematics, and experiencing intellectual joy from connecting various concepts stimulates internal motivation to study mathematics.

③ [The concept of chasing one's own tail] has been revised.
The concepts were linked based on subtopics, reflecting the change in textbook order by grade level.
I wanted to show micro-concept connections by making the connections between concepts more dense.
Of course, the macroscopic connections that go beyond units or grades remain intact.

2.
For six years of elementary school math, one well-made dictionary is enough!

● If a 'math emergency' occurs at home or in class, unfold it!

Children use dictionaries when studying English.
By using the words and idioms in the Korean-English dictionary, you can understand the meaning of sentences in English to some extent.
However, even though the math is written in Korean, there are times when it is difficult to understand what it means.
This is because you don't know the concept, so it's not easy to solve the problem by just looking through textbooks or reference books.
What if you had a math dictionary? You can't solve math problems if you don't know the meanings of the various concepts within them.
In such cases, if a child wants to independently identify and review a concept they don't understand, how can they obtain the necessary materials? If the material is previously covered and the relevant material is in an old textbook that has since been discarded, where should they look? Or, if they've identified a problem but don't know where to find the solution, what should they do? A math dictionary that allows children to easily find and easily explain concepts they don't understand is essential.
Just as you keep a first aid kit at home, a math dictionary that provides clear answers to your child's sudden questions is not an option but a necessity.

Memorizing formulas? No! Let's master elementary math with principles and concepts!
Will simply solving problems be enough to excel in math? If you neglect elementary math concepts, you won't be able to master middle and high school math.
『Concept Connection Elementary Mathematics Dictionary』 contains all of the contents of six years of elementary mathematics, from principles to basic concepts, through 134 questions carefully selected by the Elementary Mathematics Dictionary Team of the National Association of Mathematics Teachers.
Therefore, there is no missing part of the concepts or contents of elementary mathematics, and the 134 questions included cover all the questions that elementary school students can ask and the questions that they should consider among the concepts of elementary mathematics.

● The latest math dictionary reflecting the newly revised curriculum
『Concept Connection Elementary Mathematics Dictionary』 was created in line with the newly applied curriculum.
If you have any questions while studying with the textbook, you can immediately look them up in the newly created "Elementary Mathematics Dictionary with Concept Connection" tailored to the curriculum.

Easy and Simple Math! "30-Second Solver"
Separate from the detailed explanation of the question, there is a short quick answer called '30-second solution'.
If this part alone answers your questions, you can skip the 'I Want to Know That' part, which contains detailed explanations.
Now, both children and mothers can study math without any burden.

● Elementary math dictionary optimized for review
It contains everything a child needs to study on their own.
Don't look back at textbooks from the past.
With just the 'Navigation' that specifies the semester and unit names and the 'Concepts that Connect the Curve' that explains the connections from elementary to high school mathematics in detail, children can sufficiently review on their own.
All a mother has to do is find the content that her child is having difficulty with and show it to him.
After becoming familiar with the dictionary, children can go back and review it on their own.
First, look for the parts you are curious about in the relevant grade level. If you do not understand them well, look for the concepts of the previous level guided by 'Concepts that follow each other'. If you are curious about the expanded content, look for the concepts of the next level and read only the parts that your child needs.
Additionally, you can see the effectiveness of previewing by showing the connection with middle and high school mathematics.
Even if you go to middle or high school, don't throw away the "Concept Connection Elementary Math Dictionary."
Conversely, if you review while remembering elementary school concepts, you can easily discover where you are lacking.
There will be no case of giving up on math because you are a high school senior.

● Customized configuration according to child's level
Each child has a different level.
It covers everything from easy concept explanations for children who need to build a solid foundation to more challenging content for those who want to learn in depth.
Don't miss out on in-depth concepts through 'One More Step!', 'Bonus', and 'Ask Anything', which contain somewhat difficult content.
Of course, if your child feels burdened, you can skip it and read it.
It can be used at a level appropriate for your child's level without causing stress to them due to studying math.

3.
There is no such thing as 'supoja' in our dictionary!

■ 36.5% of elementary school students, 46.2% of middle school students, and 59.7% of high school students were found to have given up on math.
* Report on the results of a survey on school mathematics education for the 2015 mathematics curriculum revision (July 22, 2015)

When asked, “If you gave up on math, when did you give up?” 813 out of 2,229 elementary school students (36.5%), 1,272 out of 2,755 middle school students (46.2%), and 1,634 out of 2,735 high school students (59.7%) responded.
It is a very serious result that 36.5% of elementary school students, especially those who have just started learning, give up on math.
And the fact that about 60% of high school seniors are dropouts shows that the story of the 'sleeping high school senior math classroom' is not just a rumor, but a fact.

99% of parents say they are suffering because of their children's math.
A whopping 990 out of 1,000 parents are complaining that their children are struggling with math.
99% of parents are struggling with their children's math.
Moreover, the cost-effectiveness of private math tutoring is gradually decreasing.
With private math tutoring costs rising, why are more and more children giving up on math? No child hates math from the start.
What is driving our children to failure? It's the curriculum structure, which makes recovery impossible if the foundation is weak.

“Studying math in Korea is like building a tower.
It is a structure where stones are stacked one by one from the foundation, but if a problem arises in the middle and even one stone falls out, the whole structure will collapse.
As a result, I keep hearing the saying, “Math requires a strong foundation.”
But isn't that how children grow up?
If you look at schools, there are a lot of kids playing in their first year of high school.
He said he would play in advance because he would have to study for the entrance exams when he was in his second or third year.
However, if you miss math in your first year of high school, it is almost impossible to recover in your second or third year.
The same applies to elementary and middle school levels.
This is not education.
Education must be revitalizable.
But, does that mean that children, who don't have a criminal record, have to carry the burden of neglecting math for the rest of their lives?"
- [Current Affairs in] 2015.06.02.
From the interview article by Choi Soo-il, head of the Mathematics Education Forum, titled "A country where it's difficult to become a poet if you're not good at math"

■ The key to overcoming the fear of being a 'dropout' is 'elementary concepts' and review.

Mastering concepts in mathematics is very important.
In particular, you must have a good understanding of elementary mathematics concepts.
It is easy to ignore elementary concepts, but the CSAT assumes that elementary concepts are ingrained and asks questions based on that.
This is never easy.
(…) If you are a middle school student and feel like you have a weak grasp of elementary school concepts, I recommend that you keep the ‘Elementary School Math Concept Dictionary’ next to you and review it.
I'm not saying you should study the 'Elementary Mathematics Concept Dictionary' from page 1.
A concept dictionary is useful for looking up related information when a child encounters a concept he or she is unfamiliar with.
If you are a high school student, you can review by keeping a 'Middle School Math Concept Dictionary' or a middle school textbook by your side.
- [Current Affairs in] 2015.06.02.
From the interview article by Choi Soo-il, head of the Mathematics Education Forum, titled "A country where it's difficult to become a poet if you're not good at math"

The core of mathematics lies in elementary mathematics concepts.
The structure of the 'Korean-style linear mathematics curriculum' is such that if you neglect elementary school mathematics, you will not be able to master middle and high school mathematics.
The concepts that I didn't understand and just passed over because I was good at solving problems piled up and came crashing down in my third year of high school.
The reality that 60% of high school seniors fail the exam explains this well.
In particular, middle school students who have a weak grasp of elementary concepts should supplement their lack of concepts through a math dictionary.

4.
The very book that 2,200 math teachers across the country 'strongly recommended'!

The "Elementary Math Dictionary with Concept Connection" was created to save the 99% of parents who struggle with math.
This dictionary was created in early 2011 by six mathematics experts within the National Association of Mathematics Teachers, who shared the same goal of compiling a mathematics dictionary. This dictionary was produced over four years through numerous research, meetings, and revisions, and was verified by approximately 200 beta testers, including parents and teachers.
This elementary school math dictionary contains not only the educational know-how of a math expert with over 10 years of field experience and experience revising math textbooks, but also the concerns and worries of mothers and their love for their children.