Mentally adding hundreds to 3-digit numbers
Mentally add and subtract a three-digit number and hundreds
Lesson
Set out your lesson
“Mentally adding hundreds to 3-digit numbers means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.”
Bring to the table
- 20 counters
- Paper and pencil
Extra for the adult
Worked example. Start with 12 counters, remove 4, 8 remain. Write 12 − 4 = 8.
Optional challenge. For Mentally adding hundreds to 3-digit numbers, add one harder example after success.
What to notice. Keep one parent note: examples tried; results; support used. This session samples Mentally adding hundreds to 3-digit numbers, not mastery.
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Teaching approaches
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1 approach
Mentally adding hundreds to 3-digit numbers means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.
Materials: 20 counters; Paper and pencil. Adult models 12 − 4 by removing counters, then writes the difference. Child solves three subtraction problems with counters and records each difference. Done: three correct differences with counters matching the writing. Stop after the fresh check; keep optional challenge for another day.
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Practice this concept
Start practiceMentally adding hundreds to 3-digit numbers practice
Practice key ideas from Mentally adding hundreds to 3-digit numbers.
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Learning resources
Extra practice links — they do not replace Gakuva’s teaching approach.
Illustrative Mathematics · Practice link — not the full lesson
Regrouping
Before you open · source notes
Regrouping hundreds, tens, and ones supports mentally adding hundreds. Not every subtraction with regrouping drill.
Free, no sign-in. A teacher solution is on the same page, so use the student view with your child.
Before you openAsk the learner to add one hundred mentally and name the new hundreds digit.
Opening this link does not save learning or assess mastery.
Source, access and review notes
Public Illustrative Mathematics task page. The .html address responds HTTP 308 to this URL. An anonymous GET of this URL on 2026-11-12 returned HTTP 200 with no login or payment prompt. Where a teacher solution is present, it is on the same page as the student task; this check did not find a separate locked student view. An adult can use the student view section and should not read a solution aloud. Advertising was not observed in the fetched HTML text; that is not a browser, device, or ad-free guarantee. This is a paper or discussion task, not an automatically marked interactive game. Opening the link does not save practice or assess mastery. Diagrams on the page use missing or filename-only alt text, so they are not an accessible image equivalent. Accessibility still depends on an adult describing the picture.
Illustrative Mathematics. “Regrouping.” Licensed CC BY-NC-SA 4.0. External task; Gakuva does not copy, host, embed, or redistribute it.
CC BY-NC-SA 4.0 — link only
Check understanding
- Calculate 345 + 200 mentally
- Calculate 762 − 400 mentally
- Explain that only the hundreds digit changes
“Can your child quickly work out '342 + 200' or '756 − 300' in their head — knowing that only the hundreds digit changes?”
Curriculum record
- Type
- Procedural
- Subject
- Mathematics
- Domain
- Addition & Subtraction
- Age range
- Ages 7–9
Standards