1.OA.4: Understanding Subtraction

I can understand subtraction as an unknown-addend problem.

What Your Child Needs to Know

This standard focuses on helping your child understand the relationship between addition and subtraction. First graders learn that subtraction problems can be solved by thinking about what number needs to be added to make the total.

For example, to solve 10-8=?, they can think "8 plus what number equals 10?" This approach helps children see addition and subtraction as related operations and builds a foundation for algebraic thinking in later grades.

Real World Practice

Visual models and hands-on activities

Visual Models

1. Number Line

Show how subtraction can be viewed as "counting up" from one number to another. For 10-7, start at 7 and count up to 10 (3 jumps).

2. Part-Part-Whole Model

Use a circle with two parts below. If the whole is 12 and one part is 5, the unknown part (12-5) can be found by asking "5 plus what equals 12?"

3. Missing Addend Cards

Create cards with equations like "7 + ___ = 10" to show the connection to "10 - 7 = ___".

4. Counters with Hiding Cup

Show 9 counters, hide some under a cup, and leave 4 visible. Ask "How many are hidden?" to represent 9-4.

Everyday Activities

1. Snack Subtraction

Give your child 10 small snacks. If they eat 4, ask "How many more do you need to eat to make 10?" This reinforces the missing addend concept.

2. Card Game: Make It Match

Create cards with addition problems (5+3=8) and subtraction problems (8-5=3). Have your child match related facts to build fact families.

3. Hidden Toy Game

Show 7 toys, then hide some under a blanket. If 3 are visible, ask "How many are hidden?" Encourage thinking "3 plus what equals 7?"

4. Number Balance

Make a simple balance with a ruler. Put weights on one side to represent the total (e.g., 9). Put some weights on the other side (e.g., 6) and ask how many more are needed to balance.

Quick Checks

Strategies and quick activities

Strategies When Your Child Struggles

1. Use Addition to Check

When your child solves a subtraction problem like 12-5=7, have them check by adding: "Does 5+7=12?" This reinforces the connection.

2. Reframe the Question

If your child struggles with 8-3, reframe it as "3 plus what equals 8?" This often makes the problem clearer.

3. Use Concrete Objects

Use small objects to model. For 10-6, show 10 objects, then ask "How many more do we need to add to 6 to make 10?"

4. Fill-in-the-Blank Practice

Practice with equations like "5 + ___ = 9" before connecting to "9 - 5 = ___".

5. Number Bond Cards

Create cards showing number bonds (e.g., 10 split into 7 and 3) to help visualize the relationship.

5-Minute Practice Activities

Activity 1: Missing Number Cards

Create cards with equations like "6 + ___ = 10" and have your child fill in the blank, then connect to "10 - 6 = ___".

Activity 2: Fact Family Triangle

Draw a triangle with three numbers (e.g., 3, 5, 8). Practice writing the related addition and subtraction facts (3+5=8, 5+3=8, 8-5=3, 8-3=5).

Activity 3: Mystery Box

Show your child 8 small objects. Put some in a box without them seeing how many. If 3 are visible outside the box, ask "How many are in the box?"

Activity 4: Addition to Subtraction

Write an addition fact like "4 + 3 = 7" and have your child create the related subtraction facts: "7 - 4 = 3" and "7 - 3 = 4".

Check Progress

Track improvement

By the middle of the year, your child should:

  • Understand subtraction as an unknown-addend problem
  • Relate addition and subtraction with numbers within 10
  • Use addition to solve subtraction problems

By the end of the year, your child should:

  • Solve subtraction problems by thinking of the unknown addend
  • Fluently convert between subtraction and addition within 20
  • Explain the relationship between addition and subtraction
  • Use fact families to solve problems

Mastery Signs

Your child understands this concept when they can:

  • Automatically see the relationship between addition and subtraction
  • Use addition to solve subtraction problems efficiently
  • Explain how addition helps solve subtraction problems
  • Create fact families to show related addition and subtraction facts
  • Apply this understanding to solve word problems

Differentiation

Support for all learning levels

Below Grade Level

Practice problems focusing on simple addition with missing addends using numbers within 10.

📥 Download Practice Worksheet

At Grade Level

Standard practice with subtraction as unknown-addend problems using numbers within 20.

📥 Download Grade Level Worksheet

Above Grade Level

Advanced problems applying the unknown-addend approach to solve more complex subtraction problems.

📥 Download Challenge Worksheet