Finding a missing number in addition
CONCEPTUALUnderstand subtraction as finding an unknown addend (e.g. 10 − 8 = ? is the same as 8 + ? = 10)
Mastery Evidence
- Solve 10 − 8 by thinking 'what do I add to 8 to make 10?'
- Explain that subtraction can be thought of as a missing-addend problem
- Use known addition facts to solve related subtraction problems
Assessment Prompt
“Can [child] see that '10 − 8 = ?' is the same as asking 'what do I add to 8 to reach 10?' — so they can use their adding knowledge to help with subtraction?”
Curriculum Standards1 alignment
1.OA.4Common Core State Standards for MathematicsUnderstand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.
Prerequisites2
- Addition as combining or putting together twohardAges 4—6
- Subtraction as taking away or separatinghardAges 4—6
Show full prerequisite tree
- Addition as combining or putting together two hard
Unknown-addend requires understanding both addition and subtraction
- How Many in Total? hard
Understanding addition as combining groups requires knowing numbers represent quantities (cardinality)
- One-to-one counting hard
Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'
- Subtraction as taking away or separating hard
Subtraction as unknown-addend reframes subtraction conceptually
- How Many in Total? hard
Understanding subtraction as taking away requires knowing numbers represent quantities (cardinality)
- One-to-one counting hard
Cardinality principle builds on one-to-one correspondence — you must count correctly to know the last number tells 'how many'
Unlocks1
- Inverse: addition undoes subtractionhardAges 6—7