Q:

# regroup through thousands

9 tens 10 ones =
In Topics:
> 60 days ago

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writes:
9 tens + 10 ones

Which put another way is:

(9 groups of 10) + 10

and 9 groups of 10 is 90, so:

90 + 10 = 100

This problem does not require you to regroup though thousands, only hundreds.
> 60 days ago

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writes:
Hi Pmagloire,

In helping my second grader with his homework, I realized that the word “regroup” has a totally different meaning than how we learn math.  A couple of days ago, I found out that the word “regroup” could also refer to borrowing in a subtraction problem.  Instead of asking “do you need to ‘borrow’ to solve this subtraction problem”?  The instruction asked “do you need to ‘regroup’ to solve this subtraction problem?

Regarding your question, I think it can be “regroup” in 2 ways – one is addition (for up to second grade) and multiplication (for third grade and up).

9 tens can be written as:
9 * 10 = 90   OR
10 + 10 +10 +10 +10 + 10+ 10 + 10 + 10 = 90

10 ones can be written as
10 * 1 = 10  OR
1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 = 10

Adding the two numbers you just regroup together: 90 + 10 = 100