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Common Core Math1st GradeOperations & Algebraic Thinking

1.OA.4: Subtraction as an Unknown Addend

Also written as 1.OA.B.4 and CCSS.MATH.CONTENT.1.OA.B.4 · Cluster: Understand and apply properties of operations and the relationship between addition and subtraction.

Make a Subtraction WorksheetAll 21 1st Grade Math Standards

The Official Wording

Understand subtraction as an unknown-addend problem. For example, subtract 10 - 8 by finding the number that makes 10 when added to 8.

Common Core State Standards, Grade 1, Operations & Algebraic Thinking · Read it at the source · Checked October 14, 2026

What 1.OA.4 Means in Plain English

First graders turn a take-away into a missing-part question. For 13 - 9 they ask what goes with 9 to make 13, count up 1 to reach 10 and 3 more to reach 13, and land on 4 without counting back at all.

Subtraction then hangs on addition facts students already know, and counting up from 9 is far safer than counting back nine steps. In 2nd grade it becomes the quick route to subtraction facts (2.OA.2), and in 3rd grade division works the same way (3.OA.6).

1.OA.4 I Can Statements

  • I can solve a subtraction by finding the missing addend.
  • I can count up from the part I know to the whole.
  • I can use an addition fact to solve a subtraction.

1.OA.4 Worked Example

A subtraction fact solved without taking anything away, by counting up from the part you know.

Problem

Solve 15 - 7 by thinking addition.

15 - 7 as a missing part
  1. Read the subtraction as a missing part: 7 and how many more make 15?15 - 7 = ? as 7 + ? = 15
  2. Count up from 7 to the next ten.7 + 3 = 10
  3. Then count up from 10 to 15.10 + 5 = 15
  4. Put the two jumps together. That is the missing part.3 + 5 = 8
  5. Write both facts, because they say the same thing.7 + 8 = 15, so 15 - 7 = 8
Answer15 - 7 = 8

Check it: Take 7 counters from a pile of 15 and count what is left: 8. The adding-on route and the take-away route agree.

Common Mistakes with 1.OA.4

Treating the missing addend like a sum

7 + ? = 15 filled in as 22

Try this: Read the box as a question aloud, 7 and what make 15, and check by adding the answer back to 7.

Counting the starting number as a jump

Counts “7, 8, 9, 10, 11, 12, 13, 14, 15” on fingers and gets 9

Try this: Put a finger on 7 on a number line and count the hops, not the numbers, saying the first hop lands on 8.

Never linking the two facts

Solves 8 + 6 = 14, then counts back for 14 - 6 on the next line

Try this: Write fact families as triangles with 14 at the top and 8 and 6 below, and cover one corner to ask for it.

Where 1.OA.4 Fits

Comes BeforeK.OA.3Break numbers up to 10 into pairs, like 7 as 4 and 3.K.OA.4Find the number that makes 10 with any number from 1 to 9.
Alongside1.OA.8Find the unknown number in equations like 8 + ? = 11.1.OA.6Use the link between adding and subtracting to work within 20.
Comes Next2.OA.2Add and subtract within 20 fluently with mental strategies.3.OA.6Understand division as a missing-factor multiplication problem.

Practice 1.OA.4

Subtraction Worksheet GeneratorFree ToolDifferences within 20 with room beside each one for the matching addition fact, like 9 + 4 = 13 next to 13 - 9.Grade 1Within 20Answer key
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Quick Check

  1. Write 12 - 9 as a missing-addend problem and solve it.
  2. What number makes 6 + ? = 11 true?
  3. There are 14 seats in the circle and 8 children are sitting. How many seats are empty? Count up to solve.

1.OA.4: Other Names

1.OA.41.OA.B.4CCSS.MATH.CONTENT.1.OA.B.4

Common Core State Standards © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved. Official wording from the Common Core State Standards PDFs at corestandards.org, last checked October 14, 2026. The explanation, I can statements, example, mistakes and practice on this page are EMStudio’s own, written beside the official wording. They are not part of the standard.