Finding a missing number in addition
Understand subtraction as finding an unknown addend (e.g. 10 − 8 = ? is the same as 8 + ? = 10)
Lesson
Set out your lesson
“Finding a missing number in addition means asking what must be added to reach a total. Subtraction 10 − 8 asks the same question as 8 + ? = 10. If you know an addition fact, you can use it to solve the related subtraction. We will show the missing part with counters, then try without uncovering every piece.”
Bring to the table
- 10 large counters or blocks
- Paper and pencil
- A small cloth or sheet of paper to cover some counters
Extra for the adult
Worked example. 10 − 8 = ? becomes 8 + ? = 10. Two counters complete the ten, so both equations answer 2. The addition fact and the subtraction ask for the same missing part.
Optional challenge. For Finding a missing number in addition, solve □ + 9 = 14 by thinking 14 − 9, then check with addition. Optional: invent one short story for 10 − 7 and retell it as a missing-addend question.
What to notice. Keep one parent note: subtraction shown; missing-addend restatement; answer; whether a known addition fact was used; support used. A photo of counters alone cannot record the restatement. This samples a few related pairs, not full coverage of every within-10 or within-20 fact.
Share and support
Compare teaching approaches
Teaching approaches
Gakuva’s recommended starting approach is selected. You can still compare every option.
1 approach
Finding a missing number in addition means asking what must be added to reach a total. Subtraction 10 − 8 asks the same question as 8 + ? = 10. If you know an addition fact, you can use it to solve the related subtraction. We will show the missing part with counters, then try without uncovering every piece.
Spend about 12 minutes turning three subtraction prompts into missing-addend questions, solving them with counters, and explaining the link to a known addition fact.
Family records and proof options
Keep a record of your learning
Save photos, notes, and attendance. Export a proof packet for compliance or portfolio reviews.
Learning resources
Extra practice links — they do not replace Gakuva’s teaching approach.
Topmarks · Practice link — not the full lesson
Hit the Button · Number Bonds
Before you open · source notes
Find the missing partner in a bond—the same skill as a missing addend. Choose Number Bonds and an appropriate total.
Free · no login · ads · timed play
Before you openSave a Number Bonds screenshot and a parent note of two missing-number equations solved (for example 7 + ___ = 10).
Opening this link does not save learning or assess mastery.
Source, access and review notes
Unknown — link only
Visnos · Practice link — not the full lesson
Addition & Subtraction Facts
Before you open · source notes
Supplemental visual for relating a whole and parts when one addend is unknown. Cover one part and ask what is missing.
Free · no login · no ads observed
Before you openSave a screenshot and a parent note of a missing-addend question answered from the model.
Opening this link does not save learning or assess mastery.
Source, access and review notes
Unknown — link only
Check understanding
- 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
“Can your 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 record
- Type
- Conceptual
- Subject
- Mathematics
- Domain
- Addition & Subtraction
- Age range
- Ages 6–7
Standards