Regrouping twice in subtraction (3rd grade math)

I explain step-by-step how to regroup (borrow) twice in a 3-digit subtraction problem.

First we use a visual model which makes it easy to show that we need first break down a hundred into 10 tens, and then also break down one of the tens into 10 ones. Then we can subtract.

I also show this process of regrouping twice when the problem is written down in this format:

    500 + 30 + 5
  - 200 + 70 + 8
  ------------------
  

And lastly we learn how regrouping or borrowing looks like when subtracting the numbers the regular way (aka standard subtraction algorithm or the regular paper-and-pencil method), where one number is written under the other. First, you regroup one hundred as 10 tens, and add those 10 tens to the existing tens (if any). Then you regroup one of the tens as 10 ones, and add those 10 ones to the existing ones. Then, subtract.

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See also

Connection between multiplication and division

Math Mammoth Grade 3 curriculum

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