Can you convince me? How do you know? Generalisations Investigate when re-ordering as a strategy for subtraction. Eg. 20 3 10 = 20 10 3, but 3 20 10 – – – – – – would give a different answer. Some Key Questions What do you notice? What’s the same? What’s different? Can you convince me? How do you know? Subtraction
Generalisations Investigate when re-ordering as a strategy for subtraction. Eg. 20 – 3 – 10 = 20 – 10 – 3, but 3 – 20 – 10 would give a different answer. Some Key Questions What do you notice? What’s the same? What’s different? Can you convince me? How do you know? Can you convince me? How do you know? Subtraction
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