Grade 1

The Human Knowledge Project

Unit 7 — Understanding Subtraction

Welcome back!

In our last lesson, we learned about addition.

Today we will learn about subtraction.

Subtraction means taking away or finding how many remain.

We use subtraction every day.

What Is Subtraction?

Imagine you have:

8 cookies.

You eat:

3 cookies.

How many cookies are left?

8 − 3 = 5

You now have 5 cookies.

The minus sign (−) means "take away."

Taking Away

Let's try another example.

There are 7 birds sitting on a fence.

2 birds fly away.

How many birds remain?

7 − 2 = 5

Subtraction tells us what is left.

Using Pictures

Pictures help us understand subtraction.

⭐⭐⭐⭐⭐⭐

Take away:

⭐⭐

Now count what remains.

⭐⭐⭐⭐

6 − 2 = 4

Drawing pictures makes subtraction easier to see.

Using a Number Line

A number line also helps.

Start at 9.

Move backward 4 spaces.

You land on 5.

Subtraction means moving backward on the number line.

Addition and Subtraction Work Together

Addition and subtraction are partners.

If:

5 + 3 = 8

then

8 − 3 = 5

and

8 − 5 = 3

Learning one helps you understand the other.

Word Problems

Subtraction helps solve real-life problems.

Example:

Liam picked 10 flowers.

He gave 4 flowers to his grandmother.

How many flowers does Liam have now?

10 − 4 = 6

Liam has 6 flowers left.

Activity

Gather 10 small objects.

You might use:

Count all 10.

Now remove:

Each time, count how many remain.

Write the subtraction sentence.

Practice

Solve these problems.

9 − 2 = _____

8 − 5 = _____

10 − 3 = _____

7 − 1 = _____

6 − 4 = _____

Now create two subtraction problems of your own.

Review

Today you learned:

Every subtraction problem tells a story about what remains.

Looking Ahead

Next we will combine addition and subtraction to solve even more interesting problems.

You will learn how mathematicians choose the correct operation by carefully reading and thinking.

Every problem is another opportunity to strengthen your reasoning skills.