Operations and algebraic thinking
1.OA.D.8
Determine the unknown number in an addition or subtraction equation.
Practice for this standard
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Addition
Sums within 10 through multi-digit column addition with regrouping, plus the fact fluency underneath.
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Subtraction
Taking away, counting up, and multi-digit subtraction with borrowing across zeros.
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Pre-algebra
One-step equations with a letter in them, and undoing an operation to solve.
Official wording and the full standard: CCSS.MATH.CONTENT.1.OA.D.8