Addition and Subtraction

Introduction to Subtraction

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#### Lesson 4: Introduction to Subtraction

### What is subtraction?

#### Try This!

#### The Equals Sign

### Writing Expressions

#### Try This!

### Solving Problems

#### Ways to Count

#### Try This!

#### Number Lines

### Practice!

#### Set 1

#### Set 2

#### Set 3

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**Subtraction** is taking things away. When you have an amount and you **subtract** from it, the amount becomes smaller. Subtraction happens a lot in real life.

As we saw, if you have 8 eggs and **subtract** 3 of them, you'll have 5 eggs left. In other words:

8 - 3 = 5

8 - 3 = 5 is a** mathematical equation**. You could read it like this: five minus three equals two. As we learned in Introduction to Addition, a mathematical equation is basically a **math sentence** that uses numbers and **symbols**. When we write a subtraction equation, we use two symbols: - and =.

The **minus sign** (-) means one thing is being subtracted from another. This is why we put it after the first group of eggs — we had 8 eggs and subtracted 5 of them.

Fill in the blanks in the expressions below.

The other symbol in our equation is the **equals sign** (**=**). As we learned in Introduction to Addition, the equals sign means two numbers or expressions are **equivalent**, or **equal**. Even though they might look different, they **mean the same thing**.

In our eggs example, since 3 eggs were left, we wrote 3 to the right of the equals sign. That shows each side means 3. 3 eggs on the left, and the number 3 on the right. Both sides are equal.

As you become more comfortable with reading and writing mathematical expressions, you might notice they are useful for seeing the amount you start with and what you're subtracting.

**Any subtraction problem can be turned into a written expression**. For instance, let's say your tomato plant has seven tomatoes and you pick four. To figure out the number of tomatoes that are left on the plant, you might write an expression like this:

7 - 4

The expression is just another way of describing the situation: **seven **tomatoes minus **four **that were picked.

Write these situations as mathematical expressions. Don't solve the problems yet — simply set them up.

You have a pie with **eight** pieces. You eat **two** pieces.

You have **nine** cans of soup and you donate **seven** to the food bank.

You've gathered **six** sticks for your campfire. You throw **three** sticks on the fire.

In Introduction to Addition, you learned how to use **counting** to solve addition problems. That skill can also be used to solve subtraction problems.

We're going to take a look at two ways you can use counting to subtract. First we'll count with **objects**.

Solve these expressions.

7 - 2 =

6 - 3 =

5 - 4 =

Another way to solve subtraction problems is to use a **number line**.

Practice these subtraction problems. There are **3** sets of problems. Each set has **5** problems.

3 - 2 =

4 - 0 =

5 - 1 =

2 - 2 =

4 - 3 =

6 - 4 =

7 - 6 =

9 - 3 =

4 - 4 =

9 - 1 =

10 - 5 =

8 - 4 =

7 - 3 =

9 - 6 =

6 - 1 =

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