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Day 19 · Regroup across a zero to subtractYear 3 Maths · T1 W3–4 · Day 19 lesson

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Year 3 / Mathematics / Term 1 / Weeks 03 04

Part of the full two-week lesson sequence. Check the pack guide and taught point before teaching.

Open for this lesson: Pack guide · Aids and text routes.

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Code: AC9M3N03 (partial). Goal: solve a three-digit subtraction with transparent exchanges and verify by addition. Prepare: H/T/O cards, open number line.

  1. Invite · 2. Show 705 − 368; ask whether an answer over 705 could be sensible, and why the empty tens place matters.
  2. Model · 5. Start 7H 0T 5O. Exchange one H for ten T, then one of those T for ten O: 6H 9T 15O. Remove 3H 6T 8O → 3H 3T 7O = 337. Check 337 + 368 = 705.
  3. Guided · 6. Work 602 − 157 together. Exchange to 5H 9T 12O; subtract → 4H 4T 5O = 445. Draw the exchange arrows rather than saying “borrow”.
  4. Choice · 6. Choose one D19 card. Learner may use exchange cards or count up from the smaller quantity. Check by addition and name the unit.
  5. Exit · 4. Solve 503 − 268; expected 235. If a learner says 345, rebuild the hundred-to-ten and ten-to-one exchanges one at a time.
  6. Note · 2. Record whether the child conserved the total during exchanges and checked independently.

Access/home/extension: Use labelled, touchable groups; a scribe may move pieces only as directed. At home, use invented quantities of blank cards. Extension: count up 368→400 (+32)→700 (+300)→705 (+5), total 337, and compare with regrouping.

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