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If you were doing 3005 - 1467

Discussion in 'Mathematics' started by MasterMaths, May 8, 2011.

  1. So do you mean if we were doing it or if we were teaching it?
    Doing - I'd round and then adjust
    Teaching - the rather long "right to left" method as above (unless I was teaching some "mental methods" in which case I'd go for the round then adjust approach).
  2. You see ... even teaching, I would borrow 1 from 300 and make it 299
  3. doing ... I borrow and pay back ... every time
  4. Unless I would round [​IMG]
  5. But would you do that if you hadn't already established that it's just a shortened version of the "trying" to borrow from the first (from the right) 0, then moving to the second, then finally the 3?
    I think jumping straight in to that would be confusing wouldn't it? I guess it depends on what ability level you are teaching?
    (As you possibly know, I'm training and have far less experience than you ... I've also never had to teach this as a new skill ... so my views could be way off the mark - but thought I'd share anyway!)
  6. True
    I teach secondary so they will have seen the idea before
  7. I also teach secondary ... so they also will have the seen the idea before ... yet still have some GCSE pupils who claim never to have done it in their life and think it's some weird alien mystery! Oh the joys!!
  8. [​IMG]
  9. lancsHOD

    lancsHOD New commenter

    If not doing it mentally I would do it as DM described, myself or when teaching....
    However recently teaching a grade D student who was really struggling with number and on the first page of a past paper I decided best strategy for her was to start at 1467 and add on until she got to 3005. Think arrows add to 1470....add to 1500......... At this late stage and a few lessons left until her GCSE exam she can get the right answer this way and has no clue about decomposition!

  10. bombaysapphire

    bombaysapphire Star commenter

    I teach "counting on" as a method to find differences in my bottom sets. In angle calculations and finding change you usually have to borrow so it is easier to find the difference by counting on. I start by writing the two values at either end of a number line and adding up to the nearest 10, nearest 100 etc.
    It is what I would do in my head but writing it on a numberline makes it more accessible.
    I also teach column subtraction with borrowing as that can be easier in some situations.
  11. lancsHOD

    lancsHOD New commenter

    I notice a lot of my students automatically will add on when calculating missing angles. I tend to treat that as a 'mental strategy'. Bombay I think I may well give some weaker students the number line to help them now you've mentioned it. Thank you.
  12. I find this discussion really interesting as I teach in primary but am a maths specialist and trained to teach KS2 and 3.

    In primary, we teach children a range of methods (counting on or back on a numberline, expanded columns and standard column algorithms) and encourage them to work through the following process when meeting a calculation:
    1). Can I do it mentally?
    2). Can I do it mentally with jottings? (Including a numberline)
    3). Can I use a written method?
    4). Do I need a calculator?
    Personally, for this question, I would expect my year 6 children to do this mentally (some with, some without jottings).

    As secondary teachers, is this what you would prefer or would it be preferable to have all children proficient in standard column methods?
  13. DM

    DM New commenter

    I don't care HOW they do it, just that they CAN do it.
    By the time they reach us, at least one quarter can't. They probably still won't be able to do it when they leave us.
  14. I'm of the same opinion... there are some children who just DON'T get it no matter how many times we look at it/how many different strategies we try! It's frustrating!
  15. 3005 - 1467. Change 3005 to 2999, allowing for being 6 under.

    Now 2999 - 1467 = 1532 (no borrowing or crossing off) then add 6 = 1538

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