This is a beginner lesson for adding two 2-digit numbers with regrouping (aka CARRYING) — meant for 2nd grade math.
I first show the process alongside a visual model of base ten blocks, and then we practice it without it.
Later in the lesson, I show a problem where the answer is more than 100, requiring three digits in the answer (but the addends are two-digit numbers).
We also solve a word problem involving addition of three numbers.
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Math Mammoth Grade 2 curriculum