• billwashere@lemmy.worldEnglish
    0·
    10 days ago

    Multiplication is commutative dipshits.

    A x B = B x A

    So 1.1 x .9 is always going to be .99, regardless of the order. Didn’t we learn this in like middle school?

    (Edit … to be clear I’m calling the people in the image dipshits, not the people commenting here).

      • billwashere@lemmy.worldEnglish
        0·
        9 days ago

        If you increase something by 10% you’re doing this:

        (10% • X) + X

        (.1 • X) + X

        1.1 • X

        So you’re just multiplying the original value by 1.1. Similarly for subtracting 10% you’re multiplying by .9

        So the order in which you add or subtract 10% doesn’t matter. You always get the same number.

        • Ostrakon@lemmy.world
          0·
          9 days ago

          I have 100 dollars. I lose 10% of it. I now have 90 dollars. Now I increase my 90 dollars by 10%. Is it your assertion that 10% of 90 is 10?

          • billwashere@lemmy.worldEnglish
            0·
            9 days ago

            No. Because increasing 90 by 10% is:

            90 • 1.1 = 99

            Percentage is relative to current value, not previous calculations. 10% of 90 is 9.

    • ColeSloth@discuss.tchncs.de
      0·
      8 days ago

      You want concerning…talk to teachers about gen alpha. They can’t read well, their grammar sucks, they can’t use PC’s, they’re super gullible and believe/want to purchase whatever online influencers tell them to, and just believe whatever pops up at the top of their search result or AI says.

      • Nosavingthrow@lemmy.world
        0·
        8 days ago

        I am not convinced Alpha is unique in their gulliblity and think we should all be hesitant to believe anything we hear online about how bad ‘the youths’ are.

  • adarza@lemmy.caEnglish
    0·
    10 days ago

    pegglegg back in fifth grade: ‘why i need to learn this math stuff. i aint never gunna use it’

      • adarza@lemmy.caEnglish
        0·
        10 days ago

        you still need to know what buttons to push on the magic box, and in what order…

          • nomy@lemmy.zipEnglish
            0·
            9 days ago

            “It’s not like you’ll regularly have a little box in your pocket with access to the sum of all of the knowledge in the world but you’ll have to sift through an equal amount of incorrect knowledge and have the ability to differentiate the two.”

  • JohnDClay@sh.itjust.works
    0·
    10 days ago

    It’s only the same if it’s up 10% compared to the original number. It all depends on your time period, you could be up 30% compared to 7 years ago.

    • uranibaba@lemmy.world
      0·
      10 days ago

      Tesla stock prices are good example of this. They are down ~50% since december and up ~70% since lowest point in april last year.

    • jonne@infosec.pub
      0·
      10 days ago

      I mean, he was right about what AI was about to do. Expecting everyone to be able to live on $1000/month and not taking about the huge concentrations of wealth and power was the idiotic part.

      • oo1@lemmings.worldEnglish
        0·
        9 days ago

        TLDR - The use of notation is poor - I’d call it sloppy. His post would be much better (to me) without the example.

        Most alarmingly he’s written an inequality as an equality, and he’s not really explaining the units / percentages at all. I think this type of thing is really unhelpful to people who struggle with maths and maths notation. It seems evident that the last reply’s author does struggle and the example is part of their confusion, it certainly didn’t help.

        It makes me think he doesn’t give a shit what he writes or about the audience. That makes me inclined to give no shits about it too. Either way this style of communication is all red flags to me - I guess thats why I avoid all this twittery in general.

        Anyway, I guess I care enough to type a few more shits . . . I’m sure i’ve already put in way more thought than the OOP . . . I think he should have written something that spells out a bit more what is going on , and used an inequality, like:

        • 100 - 100 x (10/100) != 90 + 90 x (10/100)
        • 100 - 100 x (10/100) > 90 + 90 x (10/100)

        Or:

        • 100 - 100 x (10/100) = 90
        • 90 + 90 x (10/100) = 99

        As others have pointed out, in some contexts (like price indices) people convert time series data into indexes where 1 unit is referenced to: 100*1/(nominal reference price)

        So for units defined as “percent of reference price”, we d can use the simple expressions:

        • 100 - 10 =90
        • 90 + 10=100 (edited my own slop)

        Some people might, also sloppily, refer to the 10 as a “percent change” as shorthand for the units. It is a percentage, but one should be clear percent of what.

        If the context is more specifically weighted price indices then it can get more complex, but commentators may simply by saying “up by 10%”, when it’s really a more complex index value movement where the weightings can change. This all makes financial data in particular very confusing to those who struggle with maths, which is bad and it’d be nice if these things were communicated in a way that makes it as easy as possible for them.

      • Soulg@ani.socialEnglish
        0·
        10 days ago

        They’re just upset they have to agree with someone they don’t like.

  • dis_honestfamiliar@lemmy.sdf.org
    0·
    10 days ago

    I might as well throw the same comment in here. You learn this pretty quickly when you bet on meme stocks. Down 90% then up 100% I can assure you, you are no where near where you started.

    • jonne@infosec.pub
      0·
      10 days ago

      Same with crypto. You’ll get a notification something went down 10%, then up again 10%, but if you zoom out you see it’s just been slowly going down on average since the last huge spike.

  • klu9@lemmy.caEnglish
    0·
    10 days ago

    Some bureaucrats in Mexico City tried this years ago.

    An important ring road had two lanes in each direction. To increase its capacity, they didn’t actually widen the road; they just repainted the lane markings to turn two lanes into three, and claimed a 50% capacity increase!

    Everyone immediately screamed about being crammed together just centimetres apart, accidents increased and the city officials quickly u-turned; they repainted to have just 2 lanes in each direction again.

    But they then tried to claim that as that was a 33% decrease, and that because they had earlier increased it 50%, that meant they had achieved a net 17% increase in the road’s capacity!

  • driving_crooner@lemmy.eco.br
    0·
    10 days ago

    This is why in forecasting and time series analysis is used the log difference, a 10% increase or decrease on the log scale gives you the same value being added or removed.

      • driving_crooner@lemmy.eco.br
        0·
        9 days ago

        Not really, you do t=n and t=n+1, for n= 1, 2, 3 for a quick view on volatility.

        Then ypu look up for correlations between e[t=n | t= 0, t= 1…] for different Ns. For more I would need to check out my notes

        • embed_me@programming.dev
          0·
          9 days ago

          Oh I was imagining something entirely different. Like a simple logarithmic scale of a signal, I do not know anything about time series analysis. Should’ve kept my mouth shut

  • MacN'Cheezus@lemmy.todayEnglish
    0·
    10 days ago

    TBF Yang really did write the equation in the sloppiest way possible.

    Like I know what he MEANS but no math professor in the world would let this shit slide.

    • Hotzilla@sopuli.xyz
      0·
      9 days ago

      Yeah if you put it:

      100 - (100 x 0,1) = 90

      90 + (90 x 0,1) = 99

      It comes quite obvious. And I know the brackets are redundant, but my coder mind forces brackets to all math formulas for readability.

      Was it on purpose, maybe.

      • OCATMBBL@lemmy.world
        0·
        9 days ago

        Readability is important. I do the same thing, because just because something is technically correct doesn’t mean there isn’t a better way to do it. I’m very pro-bracket.

      • MacN'Cheezus@lemmy.todayEnglish
        0·
        9 days ago

        Even

        100 - 10% = 90

        90 + 10% = 99

        Works better than what he did, because that’s how you’d enter it on a standard calculator.

        • MisterFrog@lemmy.world
          0·
          9 days ago

          100 - 10/100 ≠ 90

          I’m not a fan of this at all and wish people would treat percentages as if they were a unit. x% is x of y per 100 total.

          x% = x yi / 100 ytotal

          Where yi is the species in question.

          My cup is 90% full: My cup contains 90 unitswater / per 100 unitscup

          This is why I don’t like Baker’s percentages. I guess it makes sense, because it’s still per cent, but they’re mixing the meaning used practically everywhere else these days.

          50% water for baking isn’t 50 unitswater / per 100 unitsdough, it’s 50 unitswater / per 100 units**flour**. In my mind that means you have 33.33% hydration, not 50%…

          Just feels weird to not express that as a ratio. But I guess it’s a shorthand that works for them :/

          • MacN'Cheezus@lemmy.todayEnglish
            0·
            9 days ago

            Yes I understand all that but I’m telling you standard calculators literally work that way.

            Just launch the calculator app on your phone or computer and give it a try, you’ll see.

            • MisterFrog@lemmy.world
              0·
              8 days ago

              This is very upsetting

              Thanks for the heads-up. I would have been happier never knowing haha

              The implied brackets. THE IMPLIED BRACKETS!! The horror.

              Thanks for the response kind soul

              • MacN'Cheezus@lemmy.todayEnglish
                0·
                8 days ago

                No worries. Yeah I get that it’s a bit weird if you know how to do it properly but it’s actually a fairly helpful trick for quickly calculating discounts, which I assume is the indented use. Remember, calculators were designed for lazy business folks who suck at math.

                This is exactly how someone who failed HS math would think about the problem, and conveniently, it just works.

            • Abnorc@lemm.ee
              0·
              8 days ago

              I never used the percent button, lol. I am not about to start. Something about this doesn’t jive with my soul.

          • MacN'Cheezus@lemmy.todayEnglish
            0·
            9 days ago

            Sure can.

            And yes I was stunned as well when I learned it, because that’s not how it’s taught in schools. I used to do exactly what the previous commenter did, and then one day I saw some illiterate mouthbreather type it in like that and I was like “nuh-uh, that’s not how that works, gimme that thing and let me show you.” And I typed it in the long and “correct” way, and whaddayaknow? Same result.

            But it makes sense when you think about it, calculators were literally invented for business use (and most business people are notoriously bad at math), and one of the most common uses in business is figuring out how much something should cost after applying a discount.

              • MacN'Cheezus@lemmy.todayEnglish
                0·
                9 days ago

                It works on both. I tried the calculator apps on iOS and Windows and they both worked that way. And if you still have a regular old digital calculator, it should work on that too.

  • Deathray5@lemmynsfw.com
    0·
    10 days ago

    What’s it called when you “tether” a certain value at 100%. Often for economic graphs. In that case the second guy could be correct and if that’s all they know it would make sense