Addition and Subtraction Within 20

Welcome to the World of Numbers!

Hi there, young mathematician! Today, we are going on an adventure to learn all about Addition and Subtraction. These are like "magic tools" that help us count our toys, share snacks with friends, and understand the world around us. Don't worry if this seems tricky at first—everyone starts as a beginner, and with a little practice, you will be a number superstar!

In this chapter, we will learn how to add and subtract numbers up to 20. Let’s get started!

1. Addition: Putting Things Together

Addition is what we do when we want to find out how many things we have in total. Think of it like a party where more friends keep arriving! When we add, our number usually gets bigger.

The Special Symbols:
• The plus sign \(+\) means we are putting things together.
• The equals sign \(=\) means "is the same as." It tells us the final answer.

Example: If you have 5 red apples and your friend gives you 3 green apples, how many do you have now?
We write this as: \(5 + 3 = 8\).

Cool Strategies for Adding

A. Counting On: This is a great trick! Start with the bigger number and "count on" using your fingers or a number line.
To solve \(7 + 4\):
1. Start at 7 (keep it in your head!).
2. Count 4 more: 8, 9, 10, 11.
3. The answer is 11!

B. Making Ten: It is very easy to add numbers to 10. If you have \(8 + 4\), think of it like this:
1. 8 needs 2 more to become 10.
2. Take 2 from the 4. Now you have 10 and 2 left over.
3. \(10 + 2 = 12\).

C. Using Doubles: If you know your doubles, adding is fast!
• \(5 + 5 = 10\)
• \(6 + 6 = 12\)
• \(7 + 7 = 14\)

Quick Review: Addition means "plus" or "altogether." We use the \(+\) sign to join groups together.

2. Subtraction: Taking Things Away

Subtraction is when we take some things away from a group to see how many are left. Think of it like eating some delicious cookies from a jar! When we subtract, our number usually gets smaller.

The Special Symbol:
• The minus sign \(-\) means we are taking away.

Example: You have 10 stickers and you give 4 to your brother. How many do you have left?
We write this as: \(10 - 4 = 6\).

Cool Strategies for Subtracting

A. Counting Back: Start at the big number and count backwards.
To solve \(12 - 3\):
1. Start at 12.
2. Count back 3 spots: 11, 10, 9.
3. The answer is 9!

B. Use a Number Line: Find the big number on the line and hop left (backwards) to find the answer.

C. Think Addition: Subtraction is the opposite of addition. If you know that \(5 + 2 = 7\), then you automatically know that \(7 - 2 = 5\)! It’s like a number family.

Did you know? If you subtract 0 from any number, the number stays exactly the same! \(15 - 0 = 15\). It’s like having 15 toys and giving away zero—you still have all your toys!

Quick Review: Subtraction means "minus" or "how many are left." We use the \(-\) sign to take items away.

3. Fact Families (The Number House)

Numbers like to hang out in "families." A Fact Family is a group of math facts that use the same three numbers. This helps us see how addition and subtraction are best friends.

Example: The 3, 4, and 7 family:
• \(3 + 4 = 7\)
• \(4 + 3 = 7\)
• \(7 - 4 = 3\)
• \(7 - 3 = 4\)

Key Takeaway: If you know one addition fact, you actually know three other facts too! Addition and Subtraction are inverse operations—they undo each other.

4. Common Mistakes to Avoid

1. Mixing up the signs: Always look closely to see if it is a \(+\) (plus) or a \(-\) (minus).
2. Forgetting to count the starting number: When counting on or back, don't count the number you start with. Start counting on the next hop!
3. Rushing: It is okay to use your fingers, blocks, or draw little circles to help you. Even the best mathematicians use tools!

5. Summary and Tips for Success

• Addition is for joining groups together (\(+\)).
• Subtraction is for taking things away (\(-\)).
• Number Bonds are pairs of numbers that make a certain total (like 8 and 2 make 10).
• Use a Ten Frame or a Number Line if you get stuck.
• Double-check: You can check a subtraction answer by adding the two smaller numbers back together!

You've got this! Mathematics is just like a game or a puzzle. Keep practicing your numbers up to 20 every day, and soon you'll be doing these sums in your sleep. Great job today!