Inverse: addition undoes subtraction
CONCEPTUALRecognise and use the inverse relationship between addition and subtraction to check calculations and solve missing-number problems
Mastery Evidence
- Check 15 + 7 = 22 by calculating 22 − 7 = 15
- Use the inverse to solve: □ + 9 = 14, so □ = 14 − 9 = 5
- Explain that addition and subtraction 'undo' each other
Assessment Prompt
“If [child] works out 13 + 5 = 18, can they immediately use that to say '18 − 5 = 13' — without having to work the subtraction out all over again?”
Curriculum Standards2 alignments
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.
Maths/Y2/AS/9The national curriculum in EnglandRecognise and use the inverse relationship between addition and subtraction and use this to check calculations and solve missing number problems.
Prerequisites1
- Finding a missing number in additionhardAges 6—7
Show full prerequisite tree
- Finding a missing number in addition hard
Inverse relationship builds on understanding subtraction as unknown-addend
- 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'
Unlocks3
- Unknown in Addition & SubtractionsoftAges 6—7
- Connecting RepresentationssoftAges 6—7
- Estimating by roundinghardAges 7—9