Codes: AC9M7N06, AC9M7N05. Goal: add and subtract decimals while respecting place value and checking an estimate. Prepare: fictional receipt card in materials.
- Estimate · 2 min. “$12.75 and $8.60 should total around $13 + $9 = $22. What exact total?”
- Model · 5 min. Align decimal points and cents:
12.75 + 8.60 = 21.35. Say: “Five cents plus zero cents remains five; seven tenths plus six tenths makes thirteen tenths, so we exchange one unit.” Confirm total is close to $22. - Guided balance · 6 min. If a person had $25.00, subtract $21.35 → $3.65. Check
21.35 + 3.65 = 25.00. Explain cents are hundredths of a dollar, not free-floating digits. - Pair practice · 7 min. Solve
$42.30 − $17.85 = $24.45with a place-value sketch or written method, then verify by addition. A ready pair creates a different fictional receipt and checks it. A calculator may confirm after a shown method. - Context check · 3 min. Ask whether
$21.35or$213.50makes sense for two items near $13 and $9. Use estimate as an error alarm, not a replacement for exact work. - Exit · 2 min. Everyone gives
$25.00 − $21.35 = $3.65and one inverse check. Sample focus explanation.
Access: accessible monospaced decimal columns, tactile decimal marker, adult read-aloud of prices, AAC digits. Never require real spending or disclosure of family money.