You can add and subtract numbers up to 1000 in different ways. It often helps to group addends to reach a “round” ten or hundred — for example, add 3 to 27 first, then add what is left. You can round one number, do the operation, then adjust for what you changed. Expanded form (hundreds + tens + ones) lets you add or subtract by place. For exact work with larger numbers, use column form: work place by place with carrying when you add and regrouping when you subtract.
Grouping: first make a round number
Round and adjust: 298+75=(300+75)−2=373
Expanded form: 245+132=(200+100)+(40+30)+(5+2)
Columns: carry and regroup by place
Column addition (three-digit numbers)
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