Goal: exchange 89 + 1 and compare totals to 90. Prepare: eight strips, ten ones, ninth strip, Day 19 cards.
- Notice, 3: Ask how 88 differs from 80: same eight tens, eight extra ones. Predict the next two numerals.
- Model, 5: Add one to 89, count ten loose pieces, exchange to the ninth strip. Name 90 as nine tens and zero ones. Check that the amount is the same before and after exchange.
- Guided, 8: A (game-map design: eight lines of ten path dots plus seven) and B (poster collection drawing: eight bundles of ten blank posters plus nine) show 87 and 89. Learners move 87→88→89→90; trade at the end and locate all four on the chart.
- Independent, 6: C (music program graphic: nine rows of ten beat marks) shows 90. Show 90 as nine strips and as eight strips plus ten singles; explain the equivalence without recounting all 90 marks.
- Exit, 3: Ask what numeral eight tens and ten ones become after exchange. Key: 90. If 810 or 18 appears, revisit a familiar 29+1 exchange, then repeat with 89+1.