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What does the 'O' in 'BODMAS' stand for?

Discussion in 'Mathematics' started by shirtandtie, Aug 2, 2008.

  1. Colleen_Young

    Colleen_Young Occasional commenter

    Whether or not they have heard of BIDMAS or BODMAS (I don't think any of the variations are particularly helpful) they still get that one wrong (3*2^2 or similar) from Year 7 to Year 13! Particularly something like -3^2.
     
  2. Maths_Mike

    Maths_Mike New commenter

    I have always taught that it was just a filler to make a word. So you could have BEDMAS, BODMAS, BUDMAS, BIDMAS, BADMAS if you so wanted. All of the explanations that it stands for "of" "indices" (I) etc are just multiplications anyway. So BDMAS is all you really need. (I see Bless My Dear Aunt Sally above by a poster. I have never seen that before but it covers it)

    Copy of post 8 - sorry buy you need to know that powers, indices or whatever else you call them have higher precedence than mulitiplication otherwise 3x2^2 is would be 36 which is wrong.

    MOst children I teach have used BODMAS in which case I tells them BOTH mentioned options I.E powers Of or Order.

    But my personal preference to teach this is to give them problems with loads of brackets some necessary some not and get them to realise we need way to be able to know what to do first without using loads of brackets so we come up with a rule. The ruke can be anything as long as all mathematicians do the same thing we all get the same answer. That rule is

    Brackets First
    Then powers
    Then Division or mulitiplication
    Then Addition or subtraction

    I would also specifically quote examples as mention above involving just add and subtract.
     
  3. waikatoriv

    waikatoriv New commenter


    Of course you are right, Maths_Mike, with x and / having equality and worked out from left to right. And finally + and -, worked out from left to right too if there are both. And it should always be taught this way.
    I still don't think it is necessary to have the powers however, but that is my personal preference, because whenever there is a power it refers only to the number or letter that it is attached to. So with 4 + 5y^2 you wouldn't work out 5 times y first and then square it (unless there was a bracket of course), because only the y is squared, and that is of course a multiplication. Lots of examples should be shown of cousre and problems given as you rightly suggest
     
  4. Maths-Mike: I can't work out whether in your post 21, where you refer to my post 8, you are disagreeing with what I said or not. I think I agree with what you say in post 21.

    waikatoriv: But isn't the 'equal priority' thing an unnecessary complication if you work with BIDMSA, as I suggested in post 8?
     
  5. Maths_Mike

    Maths_Mike New commenter

    yes and it should really be obvious that the power only applies to the base number it is attached to so I accept your generla point and maybe it would be easier for most children if we did not mention it and left it as common sense!
     
  6. I don't like confusing/ambiguous rules, so I would advocate committing BXDMAS to the dustbin of failed ideas.
    I've taught a mixture of kids, some of whom had heard of that silly acronym and some who hadn't. The kids in the latter category were generally more confident and correct in their ability to do arithmetic. Some really bright kids in the former category have been very confused by previous teachers' insistence on adhering to a poorly understood version of BXDMAS.
    So yes, build arithmetic skills by loads of examples of gradually increasing complexity.


     
  7. kemevez

    kemevez Occasional commenter

    "Brackets Over Division Multiplication, Addition and Subtraction" but better to use PEDMAS for several reasons and more.
     
  8. Andrew Jeffrey

    Andrew Jeffrey New commenter

    I confess I used to mention the acronym but we usually then moved away from it fairly quickly.

    I used to cheat and say that the 'O' was pOwers (rather than 'powers of'); then they would complain that it wasn't the first letter, I would agree and that would be that. Somehow the argument itself seemed to be sufficiently memorable to help them remember that powers were calculated before everything other than brackets.
     
  9. kemevez

    kemevez Occasional commenter

    "Over" - stop making it up.
     

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