Subtraction within 20 for Grade 1

Subtraction means taking away, comparing, or finding how many are left. In Grade 1, students learn that subtraction is connected to addition and can be solved in more than one way.

What Subtraction Means

If 12 cookies are on a plate and 5 are eaten, subtraction helps us find how many are left. The answer to a subtraction problem is called the difference.

Subtraction can mean taking away, but it can also mean finding the space between two numbers.

📌

Example 12 - 5 = 7 means there were 12, 5 were taken away, and 7 are left.

Count Back on a Number Line

One strategy is to start at the first number and hop backward. For 14 - 3, begin at 14 and hop back three times: 13, 12, 11.

Number lines make subtraction visible. Students can see that subtraction moves left because the quantity is getting smaller.

📌

Example 14 - 3 = 11 by hopping back three spaces.

💡

Tip Say the starting number once, then count each hop back.

Think Addition to Solve Subtraction

Addition and subtraction are partners. If you know 8 + 5 = 13, then you also know 13 - 8 = 5 and 13 - 5 = 8.

This helps when students get stuck. Instead of counting back, they can ask: "What number goes with 8 to make 13?"

📌

Example 13 - 8 = 5 because 8 + 5 = 13.

Use Story Clues

Words like left, fewer, took away, and how many more often point to subtraction.

If 15 students are in line and 6 go inside, the problem is asking how many are left outside. That is subtraction.

📌

Example 15 students - 6 students = 9 students left outside.

📝 Key Vocabulary

Subtraction

Taking away or finding the difference between numbers

Difference

The answer to a subtraction problem

Minus

The symbol or word that shows subtraction

📐 Standards Alignment

1.OA.A.1 CCSS.MATH

Use addition and subtraction within 20 to solve word problems.

1.OA.B.4 CCSS.MATH

Understand subtraction as an unknown-addend problem.

1.OA.C.6 CCSS.MATH

Add and subtract within 20 using counting, number lines, and related facts.

🔗 Glossary Connections

Subtraction Subtraction means taking away from a group to find out how many are left. We use the − sign for subtraction. Difference The difference is the answer you get when you subtract. Minus Minus means take away. Take Away Take away means some things are removed from a group. Number Line A number line is a line of numbers that helps you count forward or backward.

⚠️ Common Mistakes to Watch For

Counting the starting number as the first hop back
Subtracting the larger number from the smaller one by accident
Choosing addition when the story is really asking how many are left

🌍

Real-World Connection Kids use subtraction when they notice how many crackers are left, how many blocks were removed from a tower, or how many more points one team needs.

🤩

Fun Fact! Subtraction problems can often be checked with addition. That is why math facts come in families.