• cerement@slrpnk.net
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      1 year ago
      • 16 is the right answer if you use PEMDAS only: (8 ÷ 2) × (2 + 2)
      • 1 is the right answer if you use implicit/explicit with PEMDAS: 8 ÷ (2 × (2 + 2))
      • both are correct answers (as in if you don’t put in extra parentheses to reduce ambiguity, you should expect expect either answer)
      • this is also one of the reasons why postfix and prefix notations have an advantage over infix notation
        • postfix (HP, RPN, Forth): 2 2 + 8 2 ÷ × .
        • prefix (Lisp): (× (÷ 8 2) (+ 2 2))
      • brian@programming.dev
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        1 year ago

        prefix notation doesn’t need parentheses either though, at least in this case. lisp uses them for readability and to get multiple arity operators. infix doesn’t have any ambiguity either if you parenthesize all operations like that.

      • 16 is the right answer if you use PEMDAS only: (8 ÷ 2) × (2 + 2)

        You added brackets and changed the answer. 2(2+2) is a single term, and if you break it up then you change the answer (because now the (2+2) is in the numerator instead of in the denominator).

        1 is the right answer

        The only right answer

        both are correct answers

        Nope, 1 is the only correct answer.

        this is also one of the reasons why postfix and prefix notations have an advantage over infix notation

        Except they don’t. This isn’t a notation problem, it’s a people don’t remember the rules of Maths problem.

            • kryptonianCodeMonkey@lemmy.world
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              That’s wrong. Multiplication and division have equal precedence, same as addition and subtraction. You do them left to right. PEMDAS could be rewritten like PE(MD)(AS). After parentheses and exponents, it"s Multiplication and division together, then addition and subtraction together. They also teach BODMAS some places, which is “brackets, order, division and multiplication, addition and subtraction” Despite reversing the division and multiplication, it doesn’t change the order of operations. They have the same priority, so they are just done left to right. PEMDAS and BODMAS are the different shorthand for the same order of operations.

              • starman2112@sh.itjust.works
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                1 year ago

                They were right but for the wrong reason. Implied multiplication–that is, a(b) or ab–often comes before explicit multiplication and division. Apparently it’s up to the person writing the equation, so the meme is intentionally and explicitly ambiguous

                • kryptonianCodeMonkey@lemmy.world
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                  They’re still wrong, in my humble opinion. I’m aware of this notion, and I’ve even had people share a snip from some book that states this as fact. However, this is not standardized and without the convention being widely understood and recognized as the standard in the world of mathematics (which generally doesn’t use the symbol (÷) at all at post-algebra levels), there is no reason to treat it as such just because a few people assert it is should be.

                  It doesn’t make sense at all to me that implied multiplication would be treated any differently, let alone at a higher priority, than explicit multiplication. They’re both the same operation, just with different notations, the former of which we use as shorthand.

                  There are obviously examples that show the use of the division symbol without parentheses sometimes leads to misunderstandings like this. It’s why that symbol is not used by real mathematicians at all. It is just abundantly more clear what you’re saying if you use the fraction bar notation (the line with numerator on top and denominator on bottom). But the rules as actually written, when followed, only reach one conclusion for this problem and others like it. x÷y(z) is the SAME as x÷y*z. There’s no mathematical or logical reason to treat it differently. If you meant for the implicit multiplication to have priority it should be in parentheses, x÷(y(z)), or written with the fraction bar notation.

                  • Tlaloc_Temporal@lemmy.ca
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                    1 year ago

                    Implicit multiplication being before regular multiplication/division is so we can write 2y/3x instead of (2y)/(3x). Without priority, 2y/3x becomes (2y÷3)•x.

                    Coefficients are widely used enough that mathematicians don’t want to write parentheses around every single one. So implicit multiplication gets priority.

                  • I’ve even had people share a snip from some book that states this as fact

                    A Maths textbook.

                    However, this is not standardized

                    It’s standard in every Maths textbook.

                    there is no reason to treat it as such just because a few people assert it is should be

                    The “few people” are Maths teachers and Maths textbook authors.

                    It doesn’t make sense at all to me that implied multiplication would be treated any differently

                    There’s no such thing as implicit multiplication

                    They’re both the same operation

                    No, what people are calling “implicit multiplication” is either The Distributive Law - which is the first step in solving Brackets - or Terms - and neither of these things is “multiplication”. Multiplication literally refers to multiplication symbols only.

                    It’s why that symbol is not used by real mathematicians at all. It is just abundantly more clear what you’re saying if you use the fraction bar notation

                    The division symbol is used - it is not the same thing as a fraction bar.

                    x÷y(z) is the SAME as x÷y*z.

                    No, it’s the same as x÷(y*z).

                    There’s no mathematical or logical reason to treat it differently

                    Terms, The Distributive Law, are why it’s treated differently.

            • 0ops@lemm.ee
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              There’s an argument to be made that implicit multiplication comes before division, resulting in the answer 1, but all multiplication? That’s wrong, full-stop. You calculate (explicit) multiplication and division in one step, left to right. Reason being that division is technically just multiplying by the reciprocal.

          • Zagorath@aussie.zone
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            No, because implicit multiplication binds more tightly than explicit. a/b© becomes a/(bש)

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                Most maths textbooks written by mathematicians.

                I don’t mean when they’re explaining “here’s how the order of operations works”. I mean in the basic way that they write more advanced problems and the answers they give for them.

                This video, and the prequel to it linked in the description, go into some detail showing who uses what convention and why.

                • Nihilore@lemmy.world
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                  1 year ago

                  Interestingly I’ve wondered if this is regional, as a fellow Aussie I learned the same as you but it seems in other places they learn the other way

                  • Zagorath@aussie.zone
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                    1 year ago

                    FWIW I went to school in Asia, using an internationally-focused curriculum, rather than going through the Australian curriculum here in Aus.

                    The video I linked includes some discussion with a calculator manufacturer who apparently is under the impression that teachers in North America are asking for strict BIDMAS, so the calculator manufacturer actually switched their calculators to doing that. Until they then got blowback from the rest of the world’s teachers, so they switched back to BIDMAS with juxtaposition being prioritised over division. The video also presents the case that outside of teachers—among actual maths and physics academics—prioritising juxtaposition is always preferred, even in North America.

                  • I’m an Australian teacher who has also taught the U.K. curriculum (so I have textbooks from both countries) and, based on these comments you mention, have also Googled some U.S. textbooks, and I’ve yet to see any Maths textbooks that teach it “the other way”. I have a very strong suspicion that it’s just a lot of people in the U.S. claiming they were taught that way, but not actually being true. I had someone from Europe claim the way we (and the U.K.) teach it wasn’t taught there (from memory it was Lithuania, but I’m not sure now), so I just Googled the curriculum for their country and found that indeed it is taught the same way there as here. i.e. people will just make up things in order not to admit they were wrong about something (or that their memory of it is faulty).

            • 0ops@lemm.ee
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              That’s exactly where the calculators in the op differ. For more examples, Casio calculators do implicit multiplication first, while ti’s treat it the same as explicit multiplication and division. I think that the latter is more predictable personally, but really you just need to know your calculator.

    • Th0rgue@lemmy.world
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      1 year ago

      Depends on the system you use. Most common system worldwide and in the academic circles (the oldest of the two) has 1 as the answer.