• TrackinDaKraken@lemmy.world
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    1 month 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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        1 month 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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          1 month ago

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

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

    • starik@lemmy.today
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      1 month ago

      It’s always as easy as multiplying the two numbers. Obviously some pairs are easier than others. 7x25=175. Not too hard. $1.75 off.

  • hperrin@lemmy.ca
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    1 month 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.

  • stickyprimer@lemmy.world
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    1 month ago

    Fuck. I had to calculate 4% of 7 a few minutes ago and didn’t know this. I say fuck because it wouldn’t have helped me anyway.

      • stickyprimer@lemmy.world
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        1 month ago

        My brain was more like “Okay it’s just seven point-fours. So what’s seven fours? 28. What’s seven point-fours? 2.8. That can’t be right. Fuck. Get a calculator.

        • qarbone@lemmy.world
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          1 month ago

          I go for finding percentage factors.

          4%? That’s just 1% * 4. 1% of 7 = 0.07 * 4 = 0.28

          14%? That’s just 10% + 1% * 4 = 0.7 + 0.07 * 4 = 0.98

          You tell me it’s decimal, then I’m gonna Decimal.

    • Jankatarch@lemmy.world
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      1 month 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.

  • taiyang@lemmy.world
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    1 month 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.

  • kryptonianCodeMonkey@lemmy.world
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    1 month 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

  • Botzo@lemmy.world
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    1 month 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 month 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 month 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 month 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 month 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 month 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 month 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 month 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.

  • SnarkoPolo@lemmy.world
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    1 month ago

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

    • MrEff@lemmy.world
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      1 month 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.

  • melsaskca@lemmy.ca
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    1 month ago

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