2 digit subtraction woes...

Discussion in 'General Education' started by AZMrs.S, Dec 1, 2011.

  1. AZMrs.S

    AZMrs.S Cohort

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    Dec 1, 2011

    We just finished working on 2 digit addition with regrouping. Now we are moving on to 2-digit subtraction with regrouping and it is not going well. Both second grades are having a really hard time understanding it. My teammate and I have agreed (our P is fully on board as well) that we will be working on this concept and really driving it home until we leave for break.

    My question is do you have any unique ways of teaching this that might help the light bulbs come on? Fun math centers to practice the skills, or any other advice? I have already shown them two different ways to do it and will do anything it takes to help them make the connection.

    Thanks in advance for your help! :D
     
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  3. 1st-yr-teacher

    1st-yr-teacher Comrade

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    Dec 1, 2011

    I use the "BBB" saying. If the bigger number is on the bottom, you must borrow".
     
  4. Curiouscat

    Curiouscat Comrade

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    Dec 1, 2011

    I suggest studying something else before starting subtraction. Our school psychologist shared research with us showing that teaching the two concepts back to back is developmentally inappropriate for this age group. I have since followed her advice and find it is much easier for them to understand.
    When I do teach it I make a big deal about the story the three little pigs. I explain that when you don't have enough in the ones place then it's like needing to borrow sugar from your neighbor. I act out going over and borrowing a group of ten from my neighbor ( a student sitting close to me). Once, I really hammed it up and went and borrowed from the second grade teacher across the hall. She came over and whined how now she only had 3 groups of ten ( or sugar) left because of the big bad wolf. Sometimes I beg my neighbor for a group of tens.
    Also I have them hold their fingers to show how many ones they have. Then I ask the students to see if they have enough fingers To subtract the bottom number. If not, you better go borrow!
    Hope this helps.
     
  5. AZMrs.S

    AZMrs.S Cohort

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    Dec 1, 2011

    Good tips! Thanks! I wish we could spread it out, but our Principal is pretty stuck on following the curriculum.... I did use the borrowing analogy but I could definitely ham it up more! Thanks for the ideas, keep em coming :)
     
  6. **Mrs.A**

    **Mrs.A** Comrade

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    Dec 1, 2011

    I posted this on another thread awhile ago...It can easily be used for two digits.

    I had a couple of fourth graders who were still having a hard time with subtraction this year...I used the noun/adjective method and they really seemed to get it. This is how I had them set up the problems...

    4 hundreds 2 tens 6 ones
    - 2 hundreds 4 tens 8 ones
    _____________________________

    Of course, everything should line up... I had them do all the regrouping before they started to subtract. It really seemed to help.
     
  7. DizneeTeachR

    DizneeTeachR Virtuoso

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    Dec 1, 2011

    When I subbed a teacher used....for like
    42
    -29
    There are 9 people (or hot dogs I don't remember) and there are only 2 hot dogs (or buns), so they have to borrow from their neighbor 4 ... 10 hot dogs (or buns) to make sure they have enough. It really seems to click for many...
     
  8. czacza

    czacza Multitudinous

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    Dec 1, 2011

    More on the top
    Don't need to stop
    More on the floor
    Go next door and get ten more
     
  9. MissJill

    MissJill Cohort

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    Dec 1, 2011

    That's cute!


    I like to show my kids how after we regroup we can add up what is in each place value to the original number to show it didn't change.
     
  10. Peachyness

    Peachyness Virtuoso

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    Dec 1, 2011

    First of all, have you started teaching regrouping using base ten blocks? They need to SEE why you can't take 8 away from 2. They need hands on practice before moving onto paper and pencil and cute little poems.
     
  11. DizneeTeachR

    DizneeTeachR Virtuoso

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    Dec 1, 2011

    Peachy...you are right...probably best to start out with place value mats or something along those lines.

    I do think it's good to have something that is easy for the kids to remember while teaching it as well.... For some it "sticks" better.

    When I first read this I was thinking like another poster...why are you starting this so close to a break...where you will probably have to "start" over again. Couldn't you skip ahead and work on something or just do some reviewing on stuff that may needed a little more support from earlier in the year. As the holiday gets closer the student's focus tends to "dream of sugar plums." LOL!!!
     
  12. AZMrs.S

    AZMrs.S Cohort

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    Dec 2, 2011

    Yes, we have been using base ten blocks and mats from the very beginning. We have also been using connecting cubes as "tens" so the kids can break them apart once they regroup ( our base ten rods can't be broken apart). Unfortunately we can't just wait until after break to teach it. We are doing the best we can for now and will re-teach it again in January if need be. We did more practice today and a lot more of my kids are at least starting to grasp it. It is a slow process, but once their little light bulbs come on it will be so great!
     
  13. queenie

    queenie Groupie

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    Dec 4, 2011

    As someone else already posted, we don't teach subtraction with regrouping until after Christmas break (usually in the Spring) because the kids don't seem to do well when we teach it right after teaching addition with regrouping.

    When we do teach it, we review representing numbers with hundreds boxes, tens sticks, and ones circles. We draw each number in the problem using the boxes, sticks, and circles. Then we show how to break down the tens sticks into ten ones circles and "borrow" them. We start with two digit numbers, then move on to three digit numbers. We teach zeros last!

    For example, if the problem is 76 - 28, we draw seven ten sticks and six ones circles beside the 76. Then we draw two tens sticks and eight ones circles by the 28. We explain that we can't take 8 from 6 so we have to go to the neighbor and borrow a tens stick and break it down into ten circles so we'll have enough ones circles to take away 8 of them. We show this by placing a 1 in front of the 6 because it's like adding ten to the 6 making it 16. Then we mark out the 7 and make it a 6 because we borrowed a ten stick from the 76 and now the number has 6 ten sticks and 16 ones circles. We make sure they know that the number is the same- just regrouped (or written in a new way) to make it easier to subtract.

    It might also be helpful to use dollars, dimes and pennies!
     

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