lamolina Posted April 18, 2012 Share Posted April 18, 2012 My dd8 is learning double digit subtraction with regrouping. She can do the regrouping but doesn't seem to understand why. We are using MM. I am looking for ideas for how to help her understand this in a more concrete/visual way. Any thoughts or ideas? Thanks!! Quote Link to comment Share on other sites More sharing options...
KirstenH Posted April 18, 2012 Share Posted April 18, 2012 Khan Academy has a good video about the "why" of regrouping here: http://www.khanacademy.org/math/arithmetic/addition-subtraction/v/why-borrowing-works Quote Link to comment Share on other sites More sharing options...
jeswa Posted April 18, 2012 Share Posted April 18, 2012 The author of Math Mammoth has a video on youtube that I think is helpful. Quote Link to comment Share on other sites More sharing options...
kidsnbooks8 Posted April 18, 2012 Share Posted April 18, 2012 We use play money, 10's and 1's. Then she can see that you need to trade a ten for ones. We just did 100's, 10's and 1's today and my dd got it. She had fun "going shopping":D Quote Link to comment Share on other sites More sharing options...
usetoschool Posted April 18, 2012 Share Posted April 18, 2012 We used straws bundled up in groups on a place value mat. When you regroup you can see how you break up the groups to rearrange the straws - that the 5 in 50 is 5 groups of 10 and when you "borrow" you are taking away a whole group of 10 and moving it over to the ones, making it a something-teen. Our straws came with the mat and such that I bought from Learning Company but you could probably do it just as easily with tooth picks and a piece of paper with the columns drawn on it for 10's, 100's etc. Quote Link to comment Share on other sites More sharing options...
lamolina Posted April 18, 2012 Author Share Posted April 18, 2012 Thanks for the ideas and the links, all are very helpful! We will watch those tomorrow and try playing around with regrouping real items like money or toothpicks. We just started homeschooling 5 weeks ago so just wanted to make sure I am doing this right! thanks. Quote Link to comment Share on other sites More sharing options...
Farrar Posted April 18, 2012 Share Posted April 18, 2012 The abacus was useful for us. Quote Link to comment Share on other sites More sharing options...
ErinE Posted April 18, 2012 Share Posted April 18, 2012 The author of Math Mammoth has a video on youtube that I think is helpful. Very helpful! Thanks! Quote Link to comment Share on other sites More sharing options...
lamolina Posted April 18, 2012 Author Share Posted April 18, 2012 The abacus was useful for us. I have an abacus, but, having never used one yet, I am just not sure how to use it to explain subtraction with regrouping? Quote Link to comment Share on other sites More sharing options...
ByGrace3 Posted April 18, 2012 Share Posted April 18, 2012 we used base 10 blocks. Quote Link to comment Share on other sites More sharing options...
CroppinIt Posted April 18, 2012 Share Posted April 18, 2012 we used base 10 blocks. We used base 10 blocks too, but anything will work, really. Especially real money -- dollars, dimes, and pennies -- if she already understands about that. Quote Link to comment Share on other sites More sharing options...
Mandylubug Posted April 18, 2012 Share Posted April 18, 2012 base ten blocks help tremendously. Practice regrouping with addition and teaching what adding and subtracting truly is visually. Gradually build "over ten" numbers and then just keep building. I found subtraction regrouping is better taught after addition regrouping is mastered. It was a concept one of my sons struggled with tremendously. It took days and days and hours and hours of manipulating bases ten blocks and "playing" and then one day; it all clicked! eta: I remember straw bundles when I was in elementary school and learning this process. It worked but something about the base ten blocks just seemed to make more sense in my opinion... also, money can be used Quote Link to comment Share on other sites More sharing options...
lamolina Posted April 18, 2012 Author Share Posted April 18, 2012 The crazy thing is that she seems to get it with addition, but not subtraction. But maybe she can just follow the steps easier with addition and possibly still doesn't understand what she is actually doing. Quote Link to comment Share on other sites More sharing options...
Lucy the Valiant Posted April 18, 2012 Share Posted April 18, 2012 One of my girls loved popsicle sticks in zip-lock bags (when you have 10, you can "zip the lock," but if they're loose, they don't go in a bag; then break one open when you need to borrow). Quote Link to comment Share on other sites More sharing options...
FLDebbie Posted April 18, 2012 Share Posted April 18, 2012 We use Legos here. Anything with Legos will get my son's attention these days. Quote Link to comment Share on other sites More sharing options...
FO4UR Posted April 18, 2012 Share Posted April 18, 2012 Money and base ten blocks.:iagree: For money, use just pennies, dimes and dollars. Pretend that you have to use no more than 9 pennies and 9 dimes...and stick with dollar amounts under 10 for a little while. I have _____, and I bought a book that cost ______. How much do I have left? I have a big set of base ten blocks (1/2 are blue and 1/2 pink). I start with blue and subtract the pink, going step by step - trading ones for tens and tens for hundreds as we go. Quote Link to comment Share on other sites More sharing options...
fraidycat Posted April 18, 2012 Share Posted April 18, 2012 This is where Liping Ma's book comes in handy. Getting the children to understand the "rate at which we compose a higher value unit", or in this case "decompose to a lower value unit". I highly recommend the book if you haven't read it yet. I've gone over it a few times with DD and plan to do a lot more work with it right after our break this week. Next week, I plan to incorporate composing and decomposing higher value units until she can do explain why in her sleep. Quote Link to comment Share on other sites More sharing options...
lamolina Posted June 6, 2012 Author Share Posted June 6, 2012 Thanks for all these tips and ideas. We have played around with base ten blocks and c-rods and she is quickly able to break them apart appropriately and get the correct answer. But for some reason she can't translate that back into a written numerical problem. She just doesn't see the correlation between the regrouping of the blocks and what she is doing on paper. Does this just take a lot of repetition for some kids? Should we just keep practicing with them or does anyone have any other suggestions? I am tired of making her cry! Thanks! Quote Link to comment Share on other sites More sharing options...
Rosie Posted June 6, 2012 Share Posted June 6, 2012 Try this.... http://www.educationunboxed.com/explaining_the_subtraction_algorithm.html You may need to watch some of my other videos and play with the C-rods for a while before attempting to explain the subtraction algorithm! Quote Link to comment Share on other sites More sharing options...
happypamama Posted June 7, 2012 Share Posted June 7, 2012 (edited) I had to explain this to my DD using food as an example. Bear with me here. . . The Ones column represents slices of ham on a serving tray at a party. Uh oh. 9 people want slices of ham, but you only have 3 slices available. Go get one of the cooked hams from the storage trays in the kitchen -- the Tens. Oh, good, there are 8 hams waiting to be sliced. Slice 1 into 10 slices. Add those 10 slices to the 3 on the serving tray. Now you have 7 hams waiting, and 13 slices. Give the 9 people their slices, and you have 4 left. Uh oh. People want ham so quickly that you use up the hams waiting in the kitchen. Good thing you ordered a lot of hams, but they come in bags of 10 full hams. You've got 3 full bags of 10 hams each -- that can be 300 slices, or a 3 in the Hundreds column. So open 1 bag (leaving 2 in the Hundreds column), split it into 10 hams and add those to whatever's in the Tens column, and split more of the Tens into slices (Ones) as needed. That's all it took for her to get the idea, but since she loves food (especially ham, LOL), that helped her to see how ten slices is still the same as one whole ham; it just looks different. Somehow, that made way more sense to her than using the one and ten C-rods, hundred flats, and thousand cube, though I think for my son, the rods, flats, and cube will work just fine. Edited June 7, 2012 by happypamama Quote Link to comment Share on other sites More sharing options...
lamolina Posted June 7, 2012 Author Share Posted June 7, 2012 I love the ham analogy!! I will try that one for sure. And also thanks for the c-rod videos, I have been wondering if those could be helpful to her in some other ways. We will keep plugging away! Quote Link to comment Share on other sites More sharing options...
happypamama Posted June 7, 2012 Share Posted June 7, 2012 DD did still need some practice in remembering the steps, especially when needing to borrow from the hundreds to feed both the tens and the ones, but the ham analogy did help her to understand the concept. I suppose money would work too, but I'm all about relating it to whatever the kid needs! :) Quote Link to comment Share on other sites More sharing options...
lamolina Posted June 7, 2012 Author Share Posted June 7, 2012 I am hoping that just more practice will do it. It is strange, to me, to watch her do it with c-rods without help, and then not understand how that is the same thing as on paper! But the ham sounds like more fun! Quote Link to comment Share on other sites More sharing options...
Rosie Posted June 7, 2012 Share Posted June 7, 2012 It is strange, to me, to watch her do it with c-rods without help, and then not understand how that is the same thing as on paper! Have you tried having her do each step individually with rods and then on paper? What I mean is, don't have her do it with rods and then do the same problem with paper, but have her borrow from the tens place with rods, then move over to paper and borrow from the tens place.... then subtract from the ones place with rods and then do it on paper.... then subtract the tens place with rods, then on paper. Maybe that will help her connect it better to break down each individual step.... Quote Link to comment Share on other sites More sharing options...
kalanamak Posted June 7, 2012 Share Posted June 7, 2012 We use play money, 10's and 1's. Then she can see that you need to trade a ten for ones. We just did 100's, 10's and 1's today and my dd got it. She had fun "going shopping":D Money did it for us. First we traded pennies for dimes. Then the other way. Then we did problems e.g. 20 - 3 on the place value mat we used for addition in K. Quote Link to comment Share on other sites More sharing options...
lamolina Posted June 8, 2012 Author Share Posted June 8, 2012 Have you tried having her do each step individually with rods and then on paper? What I mean is, don't have her do it with rods and then do the same problem with paper, but have her borrow from the tens place with rods, then move over to paper and borrow from the tens place.... then subtract from the ones place with rods and then do it on paper.... then subtract the tens place with rods, then on paper. Maybe that will help her connect it better to break down each individual step.... this is a great idea, that is what we are going to try tomorrow! I also watched your video on explaining regrouping which was really helpful. i think we are going to back up a bit and watch some more of your videos and then work our way back to regrouping. Thanks so much for the input. Quote Link to comment Share on other sites More sharing options...
Rosie Posted June 8, 2012 Share Posted June 8, 2012 this is a great idea, that is what we are going to try tomorrow! I also watched your video on explaining regrouping which was really helpful. i think we are going to back up a bit and watch some more of your videos and then work our way back to regrouping. Thanks so much for the input. You're welcome! Yes, backing up a bit will probably be very helpful - especially getting some mental math in there if she doesn't already know how to do that! Quote Link to comment Share on other sites More sharing options...
Carrie12345 Posted June 8, 2012 Share Posted June 8, 2012 Translating to paper - Use or make number and operation flashcards. So, for 32 - 6, you would have 3 groups of ten and two singles, with a 3 and a 2 next to it. When you break a group of 10, you would also replace the number 3 with a 2 (because now there are only 2 groups of 10) and replace 2 with 12, because now there are 12 singles. And then you can take 6 away! On paper, my rising 4th grader sometimes still needs place value dividers to keep everything moving smoothly, particularly with longer numbers and multiple borrowing steps. Quote Link to comment Share on other sites More sharing options...
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