Chapter 2: Addition and Subtraction (One digit)

Hello, Math Explorers! Welcome to a super fun adventure with numbers. In this chapter, we're going to learn about two very important ideas: addition (putting numbers together) and subtraction (taking numbers away).

Learning this is like gaining a superpower! It helps us count our toys, share snacks with friends, and understand the world around us. Don't worry if it seems tricky at first, we'll go step-by-step. You can do it!

1. What is Addition? (Putting Things Together)

Addition is simply joining groups of things together to find out how many there are in total. When we add, the number gets bigger!

Imagine you have 3 red balloons. Your friend gives you 2 blue balloons. To find out how many balloons you have altogether, you add them!

Example: 3 balloons + 2 balloons = 5 balloons in total.

Important Signs for Addition

In math, we use special signs to make things quicker. For addition, we use:

  • The Plus Sign ( + ): This sign tells us to add. You can think of it as the word "and" or "plus".

  • The Equals Sign ( = ): This sign tells us the answer. It means "is the same as" or "equals".

So, instead of writing "3 and 2 makes 5", we can write a number sentence like this:

$$3 + 2 = 5$$

How to Add Numbers

There are many fun ways to add! Let's try adding $$4 + 3$$.

Method 1: Count Objects
Gather 4 objects (like crayons) in one pile. Gather 3 objects in another pile. Now, put them all together and count them all! You will count 7 crayons.

Method 2: Use Your Fingers!
Hold up 4 fingers on one hand. Now, hold up 3 more fingers on the other hand. Count all the fingers you have up. You'll count 7 fingers!

Method 3: Count On
This is a super-fast trick! Start with the bigger number, which is 4. Now, count up 3 more numbers from there. Say "4..." in your head, then count out loud: "5, 6, 7". The answer is 7!

Key Takeaway

Addition is about combining groups. The plus sign (+) means add. When you add, you find the total or the sum, and the number gets bigger.


2. A Cool Trick for Adding!

Here's a secret that makes adding even easier. When you are adding two numbers, the order doesn't matter! The answer will always be the same.

Example:

$$2 + 6 = 8$$

...is the exact same as...

$$6 + 2 = 8$$

Think about a fruit bowl. If you put in 2 apples and then 6 bananas, you have 8 pieces of fruit. If you put in 6 bananas and then 2 apples, you still have 8 pieces of fruit! This trick is why the "Count On" method works so well if you start with the bigger number.

Watch Out!

This cool trick only works for addition. It doesn't work for taking numbers away. We'll see why soon!


3. What is Subtraction? (Taking Away)

Subtraction is the opposite of addition. It means taking things away from a group. When we subtract, the number usually gets smaller.

Imagine you have 5 cookies on a plate. You eat 2 of them. To find out how many cookies are left, you subtract!

Example: 5 cookies - 2 cookies = 3 cookies left.

Important Sign for Subtraction

Just like addition, subtraction has its own special sign:

  • The Minus Sign ( - ): This sign tells us to subtract or "take away".

So, we can write our cookie problem as a number sentence like this:

$$5 - 2 = 3$$

How to Subtract Numbers

Let's try subtracting $$8 - 3$$.

Method 1: Use Objects
Start with 8 objects (like LEGO blocks). Now, take 3 of those blocks away. Count how many blocks are left. You will have 5 blocks left.

Method 2: Use Your Fingers!
Hold up 8 fingers. Now, put 3 of those fingers down. How many are still up? There are 5 fingers left!

Method 3: Count Backward
Start with the first number, which is 8. Now, count backward 3 numbers from there. Say "8..." then count out loud as you go down: "7, 6, 5". The answer is 5!

Key Takeaway

Subtraction is about taking away. The minus sign (-) means subtract. When you subtract, you find out how much is left, and the number gets smaller.


4. The Super Special Number: Zero (0)

The number zero (0) is very special. It means "nothing" or "none". Zero has some cool rules in addition and subtraction.

Rules of Zero

1. Adding Zero: When you add zero to any number, the number stays the same!
Example: You have 6 toy cars and you get 0 more. You still have 6 cars.

$$6 + 0 = 6$$

2. Subtracting Zero: When you subtract zero from any number, the number also stays the same!
Example: You have 4 stickers and you give 0 away. You still have 4 stickers.

$$4 - 0 = 4$$

3. Subtracting a Number from Itself: When you subtract a number from itself, the answer is always zero!
Example: You have 5 pencils and you give all 5 to a friend. You have 0 pencils left.

$$5 - 5 = 0$$

Quick Review

• Any number + 0 = The same number
• Any number - 0 = The same number
• Any number - The same number = 0


5. Addition and Subtraction are Best Friends!

Did you know that addition and subtraction are related? They are opposites, and they can help you check your work! For every addition sentence, you can make two subtraction sentences. We call this a Number Family or a Fact Family.

Let's look at the family for the numbers 4, 5, and 9.

The two addition facts are:

$$4 + 5 = 9$$

$$5 + 4 = 9$$

Now, we can use these same three numbers to make subtraction facts. Always start with the biggest number!

$$9 - 4 = 5$$

$$9 - 5 = 4$$

See? They all use the same three numbers! If you know that $$3 + 6 = 9$$, you also know that $$9 - 6 = 3$$!

Did you know?

The plus (+) and minus (-) signs have been used for more than 500 years! Before that, people just used words like "add" and "take away".


6. Solving Story Problems

Let's use our new superpowers to solve some story problems! The trick is to read carefully and decide if you need to add or subtract.

Step-by-Step Guide:

1. Read the story. What is happening?
2. Find the numbers.
3. Look for clue words. Words like "in total", "altogether", "sum" usually mean ADD (+). Words like "left", "take away", "how many more" usually mean SUBTRACT (-).
4. Write the number sentence.
5. Solve it!

Let's Practice!

Problem 1:
Sam has 6 green marbles. He finds 2 yellow marbles. How many marbles does Sam have in total?

• The clue word is "in total", so we should add.
• The numbers are 6 and 2.
• Number Sentence: $$6 + 2 = ?$$
• Answer: $$6 + 2 = 8$$. Sam has 8 marbles in total.

Problem 2:
There are 9 butterflies in a garden. 4 butterflies fly away. How many are left?

• The clue words are "fly away" and "left", so we should subtract.
• The numbers are 9 and 4.
• Number Sentence: $$9 - 4 = ?$$
• Answer: $$9 - 4 = 5$$. There are 5 butterflies left.

Key Takeaway

Reading story problems is like being a detective! Look for clues to decide whether to add or subtract. You've got this!