• SnarkoPolo@lemmy.world
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    25 minutes ago

    True mathematics derives from established mathematical theory, not some farcical aquatic armored vehicle!

  • melsaskca@lemmy.ca
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    7 hours ago

    It was recently discovered that all AI everywhere was connected to the Panzer all along. /s

    • ColeSloth@discuss.tchncs.de
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      18 hours ago

      it’s very often not useful. Like, what’s 6% of 80? See. Still hard.

      Also, with the 6% of 50 example it’s easy without using this trick.

      What’s 6% of 100? 6, right? So cut 100 in half to get to 50, and cut the 6 in half to get the 3. Cut the 50 in half again and cut the 3 in half again, and you’ll also know that 6% of 25 is 1.5.

      Which also lets you know that 6% of 75 is 4.5. the 3 from the 50, plus the 1.5 from the 25. or just know to split the difference between the 3 at 50 and the 6 at 100.

      A lot of math is just tricks for a thinking process.

      • Atomic@sh.itjust.works
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        6 hours ago

        6% of 80. 1% of 80 is 0.8 0.86 is (86)/10 Which is 48/10 = 4.8

        80% of 6. I’d probably think of it as (4/5)*6 = 24/5 Which is 20/5 + 4/5 = 4 + 4/5 = 4.8

        Both are easy if you know how to visualise it. The benefit of knowing you can “reverse” it is that you can choose which method is easier for you to visualise. Which is incredibly useful for a lot of people

      • ddplf@szmer.info
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        13 hours ago

        Good luck explaining your supreme methodology to anyone that isn’t a geek.

        • ColeSloth@discuss.tchncs.de
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          11 hours ago

          It’s stupid simple… If you know 6% of one hundred is 6, then you should know 6% of 50 is 3. You just cut each number in half.

  • TrackinDaKraken@lemmy.world
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    21 hours ago

    Let’s try this on a sale item. Hmm, let’s see, the sign says 25% off $6.99. So that’s the same as, let’s say, 7% off $25. Oh, yeah, that is much easier. /s

      • LordKitsuna@lemmy.world
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        18 hours ago

        I mean if you remove the word off it works. 25% off $100 is $25 100% of 25 is 25 it’s still reversible you just let the word off confuse you

        • derfunkatron@lemmy.world
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          18 hours ago

          You could also make sure to carry “off” to both sides when you swap:

          25% off of $100 is 100% of $25 off

    • Jankatarch@lemmy.world
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      16 hours ago

      They said the water could reach up to 50% of its 1.7 meter height before causing problems, panzer tried calculating 1.7% of 50 meters from head, this is the result.

  • kryptonianCodeMonkey@lemmy.world
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    7 hours ago

    Another counter-intuitive percentage fact: A 10 percent discount and a 10 percent fee can be calculated in either order but they don’t cancel out.

    Example, 90% of (110% of 10) = 110% of (90% of 10). But neither of those is evaluates to 10. They evaluate to 9.9.

    For any percentage X, and any base value C, (100 - X)% x ((100 + X)% x C) = (100 + X)% x ((100 - X)% x C) = (100 - (X^2/100))% x C

  • taiyang@lemmy.world
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    21 hours ago

    I was waiting in a car in front of a math tutoring building and was doing the math problems advertised on their window (as one does, of course) and the 7% of 250 is indeed probably easiest as 250% of 7, aka 2.5x7, which is 17.5.

    I did it a few other ways, though. 7% of 1000 is 70, then divide by 4 for 17.5. Well, more like, divide by 2 for 35 and again for 17.5, but yeah… mental math is fun.

  • hperrin@lemmy.ca
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    24 hours ago

    6% of 50

    6/100 * 50/1

    (6 * 50) / (100 * 1)

    (50 * 6) / (100 * 1)

    50/100 * 6/1

    50% of 6

    Works for multiplying any fraction, not just percents.

    2/3 of 5 is the same as 5/3 of 2.

    2/5 of 7/8 is the same as 7/5 of 2/8.

    • MrEff@lemmy.world
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      1 day ago

      Oddly, yes.

      Percentages also add together in partials. As in 10%+5%+2% = 17%

      So, you start with the 10% by moving the decimal over 83.27 becomes 8.327

      Then add half of that (5%) to its self and get 12.49 (rounded)

      Then take the 10% number and move the decimal over once more (1%) for 0.833 and double it (from 1% to 2%) and get 1.666 and add that to your running total to get your answer of 14.16 (rounding)

      And when I calculator check this I got 14.1559.

  • Botzo@lemmy.world
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    1 day ago

    Great for calculating tips!

    Let’s see: the bill was $138.72, so I just need 138.72% of 20. And we can subtract 100% and just add the 20 back at the end, then convert the percentage to a decimal so (.3872 * 20) + 20 = 7.744 + 20 or $27.74.

    Easy!

    • [deleted]@piefed.world
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      1 day ago

      I prefer taking 10% and doubling it for a 20% tip.

      Take the total, moved the decimal one digit to the left, double it and round to the nearest dollar. I round up at the beginning and end as well which is either close enough or a dollar high if the change is small enough.

      $138.72 > 139 > 13.9 > 27.8 > $28

      Close enough!

      • valar@lemmy.ca
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        1 day ago

        I either do this, or mentally divide by 5 (how many 5s make this number?), only caring about the closest whole number - I prefer to tip in whole dollar amounts to make the math easy.

        Eg. $39.53 is about $40, 40 is 8 fives, so tip $8

        If the service wasn’t great I round down instead of up.

        • [deleted]@piefed.world
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          1 day ago

          I multiply the tip by 5 to double check my math which is how I know it comes out as a dolllar higher sometimes.

          28x5=140

    • Catoblepas@lemmy.blahaj.zone
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      1 day ago

      I always just do 10% (easy because you move the decimal one place) and then either double that or add half of it to itself for a 15-20% tip.

      • Botzo@lemmy.world
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        1 day ago

        For sure. Reversing the percentages here makes this far more difficult. I just felt we needed to shittify this post a little.

      • Waterpumpee@lemmus.org
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        1 day ago

        i just do 0. I feel like giving 20% more than agreed upon as default is crazy. I can not imagine employers giving 20% more wages just because i was doing my job? Why should i burn money?

        • Catoblepas@lemmy.blahaj.zone
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          1 day ago

          I tip because I’ve been reliant on tips before, and I know that expecting someone who is working for tips to single-handedly solve tipping culture is unreasonable. I don’t believe in solutions that punish the poorest person in the equation, especially for a luxury like dining out.

          You can already eat at places that pay a real wage to servers if you don’t want to tip.