Regrouping in addition: 10 tens is regrouped as one hundred (2nd grade math)
First I show with a visual model how, in adding two 3-digit numbers, we may get more than 10 tens, and those are then regrouped with the hundreds (we get an extra hundred). I soon tie the visual model in with the usual way of writing one number under the other.
Later in the lesson I also show what happens when we add 3 numbers, and the sum of the tens exceeds 20.
We also look at just a few mental math problems: 80 + 70, and how we can use that result to also solve 280 + 70 and 580 + 70.
Lastly there is a PUZZLE to solve, once again, which makes Mathy so happy!
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See also
Regrouping twice in addition (3 digit numbers)
Math Mammoth Grade 2 curriculum