Math

# Subtraction with Regrouping File Folder Activity

I remember the moment like it was yesterday. I was sitting in a class on how to teach math, and honestly I wasn’t thrilled. Math had never been my favorite subject in school, and I wasn’t excited about spending the next hour discussing it.

In front of us we had a collection of base ten blocks. If you are not familiar with them, they are used to help children understand place value. Cubes can represent ones, 10 cubes forming an straight line represents the 10’s place, and 100 cubes combine form a square to represent the 100’s place. Just as a side note, they can represent decimals too if you change what block equals one!!!!

Anyway, that day we were learning regrouping. As the teacher let us play with the blocks, and began to give us ideas on how to teach regrouping, a light bulb clicked on. Up until that moment, I had never understood why in the world I would cross off a number in the tens place and then place a 1 over the number in the ones place. Don’t get me wrong. I could do it in my sleep. I was a great, obedient student who did whatever her teacher told her to do. Yet it wasn’t till I got to college that I understood why a little one would appear in the ones place so I could solve the problem.

As I began teaching I didn’t want my experience to be the experience of my students. I was determined for my kiddos to understand what they were doing, and not just be able to do it. As I taught this way, I became a much better mathematician and someone who thoroughly enjoys math.

Begin by printing off the free printable, pasting it on a file folder, and then laminating it. Next grab a deck of cards (remove all cards that do not have numbers or are greater than 9), base ten blocks, and dry erase marker.

The first step is to have your students draw two cards and place them face down on the table. Discuss what this number is. N wanted to add them together when we first started, so make sure they understand that if they have a 4 and a 6 that the number is 46. Draw two more cards and make another two digit number. Discuss that for now, when we are subtracting the largest number will go on top, and then have them place the largest number in the top two spaces, and the lower number in the bottom two spaces.

Next, review place value with them. We had the number 97 as our largest number. We discussed that the 9 was in the 10’s place and therefore was not 9 by 90. The 7 was in the ones place and actually represented 7.

Once you have reviewed place value, the student now gets to fill up the base ten chart. N placed 9 longs under the 10’s column and then 7 ones in the ones column.

Now comes the fun part….the subtraction. We have actually done subtraction problems before, but always on the numbers chart. I wanted N to connect this activity with his background knowledge so our first step was to do 97 – 28 on our hundreds chart. He correctly figured out that the answer was 69. If you haven’t taught subtraction on a hundreds chart, I would highly recommend it. It gives students another option for solving problems and developing number sense. You might even find that this is a solution for a student who is struggling!!!

After we figure out the answer was 67, It became a game to see if we would get 67 with our base ten blocks. I told him the first thing we had to subtract were the ones, and that we always had to ask ourselves one question. Do I have enough ones to subtract?? In our problem, the answer was no. I then asked him where do you think we can go to get us more ones?? After some discussion and hits, he finally decided to use a ten and place it in the ones. We furthered the discussion by talking about whether or not a long should be in the ones place and what we could do about it.

This step was difficult for him. He kept wanting to put the long back in the 10’s place and then add 10 ones to ones place. We had to have a lot of conversation and some counting to see what would happen if we put the 10’s back in the tens place. Finally he understood that we could only have 97 blocks on the mat and we had to get rid of the long!!!

FINALLY, we got to subtract and he enjoyed taking off 8 ones and 2 tens.

The last step was to count up the blocks that were left. At first he didn’t get the right answer because he didn’t count the ones that were from the 10 he used. I quickly told him that those ones counted too, and this time he got 67!!!

So grab your manipultives, and have fun teaching subtraction with regrouping.

### Get your FREE file folder activity HERE.

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