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

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

  1. I thought it was 'order'; an old fashioned word for powers/indices/exponents.

    But I notice that some recent text books have it as 'of' and give the example 1/2 of 8.

    This makes no sense to me, but perhaps I'm missing something?
  2. I thought it was 'order'; an old fashioned word for powers/indices/exponents.

    But I notice that some recent text books have it as 'of' and give the example 1/2 of 8.

    This makes no sense to me, but perhaps I'm missing something?
  3. I agree about it standing for "order". I haven't seen the "half of 8" explanation, and can't understand why anyone would think that at all useful.

    I think BIDMAS, with I for Indices/Index, is a better explanation for pupils new to the concept.
  4. I was taught that it stood for 'other' which meant other things not covered which were indices.

    But I always teach BIDMAS because I think that is a silly explanation.
  5. i was taught of

    i now use bidmas
  6. the of stands for "powers Of" still pretty poor IMO

    I have seen it stand for Ordinals, Over, Other. Order is the most common and useful.

    I have also seen BIDMAS, I for indices
    BEDMAS, E for exponentials.

    Other countries use PEDMAS Parentheses, Exponents etc.
  7. bombaysapphire

    bombaysapphire Star commenter

    Picked up from here I now use Big Purple Monsters Attack for:


    Clearly it is important that the more able know that this is the same as BIDMAS but it is easier to introduce it in this way.
  8. maths126

    maths126 New commenter

    An advantage of Big Purple Monsters Attack is the equal priority given to Multiplication / Division, as well as the equal priority given to Addition / Subtraction.

    Mindless application of "BODMAS" or "BIDMAS" can cause some children to evaluate

    9 - 2 + 3

    incorrectly as 4 rather than correctly as 10.

    Over in the States I observed some notable alternatives to BODMAS:

    Bless My Dear Aunty Sally!

    Pretty Please, Dead Mice Smell Awful

    Pepperoni Pizza, Mountain Dew And Salad
    (Mountain Dew is a popular brand name of canned lemonade - not sure if we can get it here!)
  9. waikatoriv

    waikatoriv 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)
  10. lilachardy

    lilachardy Star commenter

    My year 8 class told me it stands for Other Stuff - i.e. anything that's not a bracket \ * + or -

    It works for them!
  11. I have tried using BIDMSA rather than BIDMAS recently, as that way you can just work through the operations in the order that they come. (With BIDMAS you have to worry about giving A and S 'equal priority', otherwise you get the wrong answer with something like 10 - 3 + 1 = 8.)

    However, I am not particularly keen on any of these acronymns and suspect that the whole thing may be being given an over-inflated importance in the curriculum that it doesn't deserve.
    catherinedavid likes this.
  12. lilachardy

    lilachardy Star commenter


    If they don't know about the order of operations though, they won't necessarily get the right answer to things like 3a + 7 when a = 4

    I think it is important, and that we should make sure they are confident with it!
  13. I don't really care much for BXDMAS, where X is an arbitrary vowel.
    I was introduced to this silly acronym rather late in life, certainly well after the age of consent.
    The more I think about it, the more I am convinced that it is uneccessary and dangerous.
    As cffoster says the AS suggests that adds should be done before subtracts, so that is why 9-1+4 often turns out to be 4 rather than 12.
    Just forget the acronym and give the kids many many examples of increasing complexity so that eventually they either get it or they don't. The acronym is is of no use whatsoever.
  14. lilachardy

    lilachardy Star commenter

    To clarify my post, I was meaning the idea rather than the acronym.
  15. BODMAS is very important when doing calculations on a computer, e.g. spreadsheets. I always explain that Division/Multiplication and Addition/Subtraction have equal precedence but we say BODMAS because is sounds better than BOMDAS! I also point out that where you have operators of equal precedence then you carry out the calculation left-to-right.

    When constructing formulae in Excel you need to consider BODMAS or you will get the wrong answer (it's quite interesting to get people to try a calculation like 2 + 3 x 4 on their mobile phone to see whether they get different answers). In Excel the 'O' stands for 'powers of' and the ^ operator is used for powers so 2 + 2^2 is 6 and not 16 (you would need to use (2+2)^2 to get 16).
  16. See


    for a sort of explanation.

    We didn't have any of this when I was at school but had to look into it when my daughter became home-educated. She had been taught BIDMAS at school and we are having to stick to it so that she doesn't get too confused. Maths is not her best subject.
  17. lilachardy

    lilachardy Star commenter

    The order of operations has been around for a very very long time... it's not some new gimmick!

    catherinedavid likes this.
  18. I wasn't expecting to get such a range of interesting responses to this question.

    I teach engineers, mostly young men, who do not always have a sound maths foundation (even though they are suppossed to).

    I'm thinking of using BIDS (Bl**dy Idiots Drink Snakebite).

    What do you think?
  19. weggster

    weggster New commenter

    We were taught "Other nasty things".

    This makes sense especially when you progress to solving:

    2sin(x + 20) = 0.5

    if you think of the order you compute and then work backwards for solutions it does make sense.

    I haven't found a problem (even at degree level) where this didn't make sense.

    Hope this helps, it really does enscapulate all of our functions that we use.

  20. Piranha

    Piranha Star commenter

    We do have a problem with the O standing for "Other" because of (for example) Sin 2x where we do the multiplying before the Sine function.

    Post 8; Without the I (or O), it is not clear how to handle 3*2^2.

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