Arithmetic Grade Three

Lesson Twenty-six: Step By Step Regrouping

We've already done many problems that look like this: 

   19
   +4
  ----
We can count up the answer to this problem really easily and get 23, but this is such an easy problem that it will serve to help us understand how to carry or regroup.

If we add the numbers in the ones column (9 + 4 = ) we get 13. In our answer to 19 + 4 we get 23. So when we add the numbers in the ones column and get 13 we split up the 1 and the 3 (the two digits in 13) like this: 


   1
   19
   +4
  ----
    3
Our partial sum for just the ones column is 13 (which has a 1 in the tens column and a 3 in the ones column). The 3 in the ones column of 13 is placed in the ones column for the answer. BUT the 1 in the tens column of 13 is placed above the tens column of the top addend (as shown). Next we add the numbers in the tens column (including the 1 we carried). 

   1
   19
   +4
  ----
   23
Here's another example: 

    35
   +27
   ----
Problem without answer

    1
    35
   +27
   ----
     2
Adding the 5 and 7 in the ones column we get 12. We take the 2 from 12 and place it in the ones column of the answer and we carry the 1 above the tens column above the addends.

    1
    35
   +27
   ----
    62
We add up the 1, 3, and 2 in the tens column.

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