• otacon239@feddit.de
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    11 months ago

    Nope. It’s PEMDAS at work.

    8/2(2+2)

    8/2(4) - Parentheses

    8/8 - Multiplication

    1 - Division

    Modern phone apps seem to be notorious for getting order of operations wrong. I’ve never had this issue with a dedicated calculator.

    Edit: my petard has been hoisted

    • Laser@feddit.de
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      11 months ago

      You don’t do multiplication before division, they’re equal operations, so you go left to right. 8 x 0.5 (2 + 2) is the same from a mathematical point of view.

    • Julian@lemm.ee
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      11 months ago

      I’ve always been taught that + and - were interchangeable with each other for pemdas, as well as * and /. So the hierarchy is

      • parenthesis
      • exponents
      • multiplication, division
      • addition, subtraction
    • Nightwatch Admin@feddit.nl
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      11 months ago

      In PEMDAS M does not get priority over D so the equation has to be executed in order: 8/2=4, 4*4=16. You would be correct if all PEMDAS were a priority list., but it is not.

    • TentacleKitten@lemm.ee
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      11 months ago

      Multiplication and division are same level just as addition and subtraction are same level. So it would be worked multiplication and division in order from left to right.

    • DarkMessiah@lemmy.world
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      11 months ago

      Actively wrong.

      PE(MD)(AS).

      Parenthesis comes first, do everything in each of them as though they were a whole equation to themselves.

      8/2(2+2) = 8/2(4)

      Then you do your exponents. The equation doesn’t have any, so we can go ahead and skip those.

      Multiplication and division are the same operation, just flipped around, so you go left to right and do those as you come across them. A number next to a parenthesis means multiplication, so to simplify:

      8/2(4) = 8/2x4

      8/2x4 = 4x4

      4x4 = 16

      Addition and subtraction don’t have any weird effects on the outcomes of each other, so you go left to right and do them as they come up. This equation has no more addition or subtraction to do, so we can consider what we have left our answer.

      Therefore: 8/2(2+2)=16

      This is straight from the textbook. You are wrong, and so are your purpose-built calculators.

      EDIT: Replaced * with x to avoid italicising.

      • Zagorath@aussie.zone
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        11 months ago

        Replaced * with x to avoid italicising.

        You can do this without needing to replace by using a backslash. 1*2 comes from 1\*2.

        Anyway, the problem with your logic is that it’s using rules designed for primary school by one random primary school teacher many decades ago. Not a rigorous mathematical convention.

        In real maths, mathematicians frequently use juxtaposition to indicate multiplication at a higher priority than division. Rather than BIDMAS, something like BIJMDAS might work. But that isn’t as catchy, and more to the point: it requires understanding of an operation that doesn’t get used in primary school, so would be silly to put in to a mnemonic designed to aid probably school children.

        • DarkMessiah@lemmy.world
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          11 months ago

          Just looked it up. Everything I know is a lie. Thank you, kind stranger on the internet. I’m going to go have an existential crisis, now.

        • the problem with your logic is that it’s using rules designed for primary school

          Actually The Distributive Law is taught in Year 7. The Primary School rule, which doesn’t include brackets with coefficients, is only the intermediate step.

          many decades ago. Not a rigorous mathematical convention

          It’s an actual rule which is centuries old.

          mathematicians frequently use juxtaposition to indicate multiplication

          It’s not multiplication - it’s either The Distributive Law or Terms, which are 2 separate rules.

          an operation that doesn’t get used in primary school

          Yes, as I said it’s taught in Year 7.

          • Zagorath@aussie.zone
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            7 months ago

            When I was in school, year 7 was primary school.

            Anyway, I’m the time that is relevant here is when you’ve done the various relevant mathematical tools, but haven’t yet been exposed to multiplication by juxtaposition. Which I’m fairly sure for me at least was in year 6.

            It’s an actual rule which is centuries old.

            No, the idea of specifically codifying BIDMAS comes from the early 1900s.

            I don’t know why you’re going throughout this thread over multiple hours spamming out your nonsense, but it’s wrong. BIDMAS is a convention, and a very useful one, but only because we instinctively know juxtaposition actually comes before explicit multiplication or division, and a rigid primary school application of BIDMAS will lead you to the wrong answer.

            Thankfully, I think you know that last part. Because I think that’s what you mean when you keep saying “it’s called terms”. But that, too, is wrong. It’s used in terms, for sure. y = 2x2 + 91/2)x - 4 contains three terms, the x2 term is 2x2, etc. But if I then changed the constant term to be 4(2 - 3×5) + 1, all of that would still only be the one term. Terms and multiplication by juxtaposition can work together, but fundamentally refer to entirely different aspects of mathematics. Juxtaposition is a notational thing, while terms are a fundamental aspect of the equation itself.

            • When I was in school, year 7 was primary school

              Oh really? My apologies then. I’ve only ever heard Year 7 called high school or middle school, never primary school. What country is that in?

              multiplication by juxtaposition. Which I’m fairly sure for me at least was in year 6

              I’ve seen some Year 6 classes do some pre-algebra (like “what number goes in this box to make this true”), but Year 7 is when it’s properly first taught. Every textbook I’ve ever seen it in has been Year 7 (and Year 8, as revision).

              Also, it’s not “multiplication by juxtaposition”, since it’s not multiplication - it’s The Distributive Law - which is Distribution - and/or Terms - which is a product, which is the result of a multiplication.

              No, the idea of specifically codifying BIDMAS comes from the early 1900s

              The order of operations rules are older than that - we can see in Lennes’ letter (1917) that all the textbooks were already using it then, and Cajori says - in 1928 - that the order of operations rules are at least 300 years old (which now makes them at least 400 years old).

              If you’re talking about when was the mnemonic BIDMAS made up, that I don’t know, but the mnemonics are only ways to remember the rules anyway, not the actual rules.

              I don’t know why you’re going throughout this thread

              I’m a Maths teacher, that’s what we do. :-)

              a rigid primary school application of BIDMAS will lead you to the wrong answer

              Only if the bracketed term has a coefficient (welcome to how Texas Instruments gets the wrong answer), which is never the case in Primary School questions - that’s taught in Year 7 (when we teach The Distributive Law).

              juxtaposition actually comes before explicit multiplication… I think that’s what you mean when you keep saying “it’s called terms”

              Terms come before operators, and we never call it juxtaposition, because The Distributive Law is also what people are calling “strong juxtaposition” (and/or “implicit multiplication”), but is a separate rule, so to lump 2 different rules together under 1 name is where a lot of people end up going wrong. There’s a Youtube where the woman gets confused by a calculator’s behaviour and she says “sometimes it obeys juxtaposition and sometimes it doesn’t” (cos she lumped those 2 rules together), and I for one can see clear as day the issue is it’s obeying Terms but not obeying The Distributive Law (but she lumped them together and doesn’t understand these are 2 separate behaviours).

              Terms and multiplication by juxtaposition can work together

              But that’s my point, there’s no such thing as “multiplication by juxtaposition”. A Term is a product, which is the result of a multiplication.

              If a=2 and b=3 then…

              axb=2x3 - 2 terms

              ab=6 - 1 term

              In the mnemonics “Multiplication” refers literally to multiplication signs, and nothing else. The Distributive Law is done as part of solving Brackets, and there’s nothing that needs doing with Terms, since they’re already simplified (unless you’ve been given some values for the pronumerals, in which case you can substitute in the values, but see above for the correct way to do this with ab, though you could also do (2x3), but absolutely never 2x3, cos then you just broke up the term, and get the wrong answer - brackets can’t be removed unless there is only 1 term left inside. People writing 2(3)=2x3 are making the same mistake).

    • Beefy-Tootz@lemmy.world
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      11 months ago

      My public school education on pemdas is that for multiplication/division and addition/subtraction, you do them on order from left to right. Doing it that way gets me 16, which I believe to be right, but I’m also very bad at math. The way you had explained is also technically correct, if you do the multiplication out of order. Now that I think about it, you could solve for the parentheses by multiplying 2+2 by two, giving you 8/8 quicker and still yielding 1. I’m now having more doubts about my math capabilities, both are right, but I know that’s wrong, I just don’t know why

      • you could solve for the parentheses by multiplying 2+2 by two, giving you 8/8 quicker and still yielding 1. I’m now having more doubts about my math capabilities

        No, that’s the correct way to do it, as per The Distributive Law.

        both are right

        No, only 1 is right. If you get 16 then you did division before finishing solving brackets.

    • 8/2(4) - Parentheses

      8/8 - Multiplication

      Correct steps, but wrong names. Where you said “multiplication” is actually still parentheses - that first step isn’t finished until you have removed them (which isn’t until after you have distributed and simplified, which you did do correctly).

      Modern phone apps seem to be notorious for getting order of operations wrong

      Yes, I know, and as a Maths teacher I am well and truly sick of hearing “but Google says…”, and so I wrote this thread to try and get developers to fix their damn calculators.