• Sludgeyy@lemmy.world
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      1 year ago

      1% of 33 is .33

      .33 × 7 =

      .3 x 7 = 2.1

      .03 x 7 = .21

      21 + 2.1 = 2.31

      So

      7% of 33 = 2.31

      You could also do

      33% of 7

      10% of 7 is .7

      1% of 7 is .07

      So 11% is .77

      .77 × 3 =

      .7 × 3 = 2.1

      .07 × 3 = .21

      2.1 + .21 = 2.31

  • TAYRN@lemmy.world
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    1 year ago

    …I mean, yeah? If the number is 50 or 10 that works out great. But let’s try that with 7% of 13. Now it’s 13% of 7. Just like you said, “much easier to calculate.”

    Okay, choosing prime numbers was intentionally mean on my part. But 3% of 9 becomes 9% of 3. 4% of 2 becomes 2% of 4. Can anyone honestly look me in the eye and tell me that this tip has helped them out in any meaningful way?

    • Tikiporch@lemmy.world
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      1 year ago

      Well, single digit percentages are easy. If it helps, move your decimal to the right so 9% becomes 90%. You can probably calculate 90% of 3 because you can do 10% and subtract it and get 2.7. Now move your decimal back to the left and you get 9% of 3 which is 0.27. You can do the same with higher percentages once you learn to break them in to 10% pieces.

        • Mr_Dr_Oink@lemmy.world
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          1 year ago

          This is not mental gymnastics.

          This is a coherent method and makes a lot of sense.

          Mental gymnastics is when someone has to lie to themselves to make a point that isn’t correct. Like when people argue that trump was a good president because they can list several good things he did.

          Or when people claim something is mental gymnastics when it’s actually called maths.

    • 1847953620@lemmy.world
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      1 year ago

      Yes, idiot. Choosing instances of when it’s less helpful (arguably) doesn’t negate the cases where it is deemed very helpful.

  • Marxism-Fennekinism@lemmy.ml
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    1 year ago

    Also, a surprising number of people don’t know that precentages are more often than not represented as decimals between 0 and 1 as opposed to actually a number out of 100 when used in calculations (because the concept of a percent doesn’t really exist in math, it’s just a context specific way of formatting a decimal). A lot of people just enter 69 when calculating a formula that operates on a precentage instead of 0.69 which obviously makes the formula useless, or if a formula is supposed to output a precentage, they assume that it output 0.69 percent instead of 69 percent.

  • cmhe@lemmy.world
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    1 year ago

    I thought with “reversible” they meant that a number falling 50% and then rising 50% afterwards, it is the same number, which is not true.

    10 * 50% = 5

    5 * 150% = 7.5

    • Sylvartas@lemmy.world
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      1 year ago

      Yeah the correct term would be “commutative” as someone already pointed out. Meaning the order doesn’t matter when considering multiple percentages. E.g 50% of 73% of something is the same as 73% of 50% of that same thing