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<3 (media.piefed.social)
submitted 1 year ago by to c/mathmemes@lemmy.blahaj.zone
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[–] -5 points 1 year ago (16 children)

25 - 5 ÷ 5 when read naively left to right looks like it would be "25 - 5 = 20. Then take that and divide by 5, for an answer of 4". It would be clearer to write it as (25 - 5) ÷ 5 or 25 - (5 ÷ 5) depending on what's intended.

You see those kind of "gotcha!" posts online sometimes, where someone posts a problem that tempts you into doing order of operations wrong.

Someone who sees how to do it correctly immediately and thinks everyone knows that is invited to view https://xkcd.com/2501/ as well.

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  • [–] 6 points 1 year ago (12 children)

    Natively? It's a math equation there is only one way to read it as far as I am aware.

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  • [+] -6 points 1 year ago (9 children)

    Naively, not natively. Someone who wasn't a good math student, or just doesn't remember, might read it left to right and come to the wrong conclusion. The rules for order-of-operations are, so far as I know, arbitrary, and different people coming at it without instruction (ie: naively) could arrive at different conclusions. Knowing that you're supposed to do division first isn't obvious.

    You could read 25 - 5 ÷ 5 as "25 - 5 is 20. 20 divided by 5 is 4" or you could read it (correct, per the standard rules) as "25 minus.. hold on.. 5 divided by 5 is one. Now 25 subtract that from the 25 sitting over there, and get 24." This isn't the same kind of error as, like, "5 divided by 5 is 0"

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  • [–] 7 points 1 year ago* (7 children)

    You could read 25 - 5 ÷ 5 as "25 - 5 is 20.

    You could. You could also lower your pants and drop a massive turd and call that the answer. Both answers would be equally wrong.

    PEMDAS isn't a suggestion that you follow when it suits you, like religion. It's how math is communicated, unambiguously.

    In any case, if that's where we lost you, then I've calculated the chance of you catching the factorial as √-1.

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  • [+] -8 points 1 year ago (2 children)

    You're being weirdly aggressive, but okay.

    Most people know the symbols for addition subtraction multiplication and division. Far fewer people know the established order of operations. That's what powers those "only 3% of people solve this problem correctly!" math memes.

    But okay. Communicate badly (ie: by failing to acknowledge your audience's context) and be smug if you want.

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  • [–] 4 points 1 year ago

    Oh you're gonna love my other reply then.

    Don't expect me to pander to willful ignorance. If you're going to act like an idiot, expect to be treated like one.

    Also, what's with the passive aggressiveness? I understand that my confrontational approach there can make some people uncomfortable, but it's my prerogative.

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  • [+] -9 points 1 year ago (3 children)

    On the extremely rare occasion when I have the misfortune to be performing a mathematical calculation, I take enormous pleasure in carrying out the operations exclusively left to right unless indicated otherwise by brackets, which is the correct way to indicate this. If you want me to do a calculation separately, put brackets around it or bugger off. It’s your choice, really

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  • [–] 3 points 1 year ago (1 child)

    Many of the things we believe about ourselves and our experiences turn out to be false. Sometimes this is due to innocent memory failures or to the lack of needed information.

    Suppose that Charles believes that he failed his biology test because the professor asked obscure and ambiguous questions.
    Charles believes this because he doesn’t realize that he got the lowest score out of the 100 students who took the test, and that most people did quite well.
    If Charles had this information, he would realize that he failed the test because he didn’t study hard enough, or because he’s not very good at biology.

    On the other hand, if Charles continues to believe that the test was unfair after seeing the grade distribution, he is either severely challenged in his capacity for rational calculation or he is the perpetrator of willful ignorance.

    Which is it?

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  • [–] -2 points 1 year ago

    I literally just said I enjoy doing calculations incorrectly because I dislike the method of notation so much that I reliably and deliberately choose to misinterpret it every time.

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  • [–] 1 point 1 year ago*

    unless indicated otherwise by brackets, which is the correct way to indicate this

    No it isn't. The order of operations rules are at least 200 years older than the use of Brackets in Maths. Not sure how you think Maths was done before we started using Brackets.

    put brackets around it or bugger off.

    Bugger off with your disinformation. There are no Maths textbooks which use Brackets for such a basic expression. Students are expected to know the order of operations rules

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  • [–] 0 points 1 year ago

    The rules for order-of-operations are, so far as I know, arbitrary

    No, they're not.

    Knowing that you’re supposed to do division first isn’t obvious.

    It is if you've been to school or read a Maths textbook

    correct, per the standard rules

    The only rules

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  • [–] 2 points 1 year ago

    Hey, Munroe is a rather cool and very intelligent engineer. Very witty writer, and awful at drawing. But his philosophy is mid at best. He is not an authority, and is often wrong or common place when it comes to social topics and human affairs. He understands communication in a very techy engineering dimension. There's no need to take his comics as anything but what they are. One white dude's anecdotic commentary on his own very limited experience of the human condition. He knows squat about human communication, sociology, psychology or postmodernism.

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