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Day 11 · Estimate the size before finding a productYear 5 Maths · T1 W3–4 · Day 11 lesson

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Year 5 / 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 · Sources and materials · Worked swaps · Aids and text routes.

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Success: choose a benchmark for a larger-number product, calculate and explain why the exact result is plausible. Prepare: first model in MATERIALS, blank estimate mat. Codes: AC9M5N06, AC9M5N08.

  1. Recall · 2 min. Ask if 50×20 is a useful scale for 48×19. Key: yes, about 1,000; it is not the exact seat count.
  2. Model · 5 min. On the invented 48-by-19 stand, show 48×(20−1)=960−48=912. Both factors were rounded up for 1,000, so an answer above 1,000 would deserve a recheck. Say the original unit is drawn seats, not attendance.
  3. Guide · 6 min. Compare 246×4 with 250×4=1,000. Partition 246×4=(200+40+6)×4=800+160+24=984. Ask which estimate is intentionally a little high and why.
  4. Choose · 7 min. Offer one Day 11 A/B/C card. Ask for an estimate before exact multiplication, a visible method and one sentence comparing them.
  5. Exit · 3 min. “Would 9,120 be reasonable for 48×19?” Key: no, about ten times a useful benchmark. Repair a misplaced zero with the bound.
  6. Record · 2 min. Note estimate, exact value and explanation separately. A child's reasonable estimate can be sound even if their exact arithmetic needs reteaching.

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