Making sense of adding in column

Rosie, my 1st grader, came back from School recently talking about adding 2-digit numbers in column.

Adding in column 23 + 14 ?  3 +4 = 7, 2 + 1 = 3… so the answer is 37. Adding 37 + 44 ?  7 +4 = 11, 3 + 4 = 7… so the answer is 711. Wait, Mom. It does not make sense, doesn’t it?

Nope, Rosie, 711 doesn’t seem to make sense. So let’s step back an inch, with the Base Ten Blocks (click here if you want to read more about these blocks).

AddingA

Here is an example of 32 +23, and the connection between the blocks, and the addition in column. While adding in column, you add the Ones, then the Tens, then the Hundreds, and so on, and the blocks provide a neat concrete representation of such process. Indeed, it shows why you have to “align” digits (because if you don’t, you end up adding Ones to Tens !).

AddingJ

But what I like the most with these blocks is how they  help children  make sense of carrying an over to the next column. Here is an example with 37 +44.

AddingH

From the 11 Ones you get from the right column (i.e. the Ones column 7+4), you trade 10 Ones from 1 Ten that you carry over to the left column (i.e. the Tens column).

Here you go, Rosie, 711 does not make sense, but 8 Tens 1 Ones aka 81 does.

 


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