Subtraction within 20 for Grade 1

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. If one child has 12 stickers and another has 8, subtraction can help show how many more stickers the first child has.

This is why students should see subtraction in more than one kind of story. Some stories are about things leaving. Others are about comparing amounts. Both are subtraction because both ask about a difference.

When children connect subtraction to real situations, the symbols in an equation begin to make sense.

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. This is especially helpful for children who still need to see the movement of the numbers.

It is important not to count the starting number as the first hop. Students should put a finger on 14, then move back once to 13. That is hop one.

As children practice, they begin to notice that small subtraction facts can be solved quickly, but the number line still remains a useful tool for checking.

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?" This turns subtraction into a missing-addend problem.

For some children, thinking with related facts is faster than counting back. If they know 10 + 4 = 14, then 14 - 10 = 4 right away.

Fact families help students see that the same three numbers belong together. This builds confidence and makes subtraction feel less like a completely separate skill.

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. If one child has 15 stickers and another has 6, the question "How many more?" is also subtraction.

Students should practice reading the whole story before choosing an operation. A single clue word is helpful, but the full situation matters more.

Drawing the story or acting it out with counters can help children decide whether they are taking away, comparing, or finding a missing part.

Check Subtraction With Addition

A good way to check a subtraction problem is to use addition. If 14 - 6 = 8, then 8 + 6 should equal 14.

This check helps students notice mistakes. If the numbers do not fit back together, something went wrong and the problem should be tried again.

Checking with addition also strengthens the idea that addition and subtraction are connected operations. Instead of memorizing separate facts, students begin to see how one fact family works together.