• rumba@lemmy.zip
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    7 days ago

    You can also

    Multiply one side, divide the other to get the base number to get the base number to 100.

    6% of 50 == 3% of 100 == 3

    5% of 20 == 1% of 100 == 1

    7% of 50 == 3.5℅ of 100 == 3.5

    14% of 200 == 7% of 100 == 7

    Edit* as pointed out below, this one was incorrect.

    14% of 200 == 28% of 100 == 28

    You don’t have to stop at percentage either.

    25 * 16 = 100 * 4

    If you’re doing addition, you can add and subtract.

    27 + 13 = 20 + 20

    Most of the difficulty is in realizing that one number or the other can be brought up to a nice round number, making the equation simple to do in your head. And obviously, just getting to around number on one side doesn’t always make it easy on the other side.

    I always loved screwing with math problems to make them easier, which is weird, because overall, I don’t really care for math.

    I also do shit like borrowing a couple of numbers to make the equation easy and then pull them back out.

    392 / 4 == (400 - 8) / 4 == (100-2) = 98

    376 / 4 == (400-24)/4 =100-6=94

    Of course it goes up a level when the remainder isn’t evenly divisible. But I still find it’s something I can handle in my head.

    371 / 4 == (400-29)/4= 100-7¼ =100-7.25=92.75

      • rumba@lemmy.zip
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        6 days ago

        I would argue you’re still doing the other side just subliminally. But it is a fair point.

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        7 days ago

        Oh shit, there I go getting along winded and get lost, yep, that should have been multiplied on the other side.

    • Test_Tickles@lemmy.world
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      7 days ago

      Are you just out here doing common core math on here like it’s just some smart trick to make math easier?! You dirty bastard, some conservative is going to see this and think it’s a good idea, then they’ll just innocently do it in front of their conservative friends and all hell will break loose. Homosexual fornication will suddenly run rampant through the group and those few that can resist the call of the devils numbers will have to cull the rest. You know… Actually… I am not completely against that now that I think about it…

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        6 days ago

        Rofl, I pre-date common core. I’m not exactly sure to what extent they do all that stuff. I do know that they’ve got a fuck of a lot of numberlines, like so many number lines. Like they’re being paid by the number line.

        Back in the 80s and 90s, the teachers would do regular scrolling down arithmetic, and they would mention borrowing numbers and shortcuts. And I took that shit seriously because I did not like sitting down and adding/multiplying numbers. I’d probably spend an extra 30 seconds of problem if I thought I could not have to sit down and write equations.

        • Test_Tickles@lemmy.world
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          6 days ago

          That’s really cool. The borrowing thing is the part of common core that they teach in elementary, and it is the part that enrages conservatives. The point of the homework and practice questions is to repeatedly do the borrowing thing until it becomes automatic and something that they do in their heads all of the time. So, it absolutely enrages the right when kids get the correct answer, but lose points for doing the problem the wrong way.
          I was taught to do it the hard way and had to figure out the other tricks for myself much later in life, so now, even after decades of doing it your way, it’s more of a struggle than it should be and I just reach for my calculator instead. So I envy you quite a bit.

          Keep up the good work with your subversive teaching of common core principles as tips, tricks, cheats and shortcuts. That’s actually how they should have branded it, instead of common core, it should have been cheating core, then they would have been all for it.

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            6 days ago

            There’s nothing wrong with calculators.

            I wonder if the next generation is going to be reaching for AI for all their English needs.

            • There’s nothing wrong with calculators

              There is if you’re talking about calculators on phones, etc. Almost all of them give wrong answers to order of operations questions because the programmer didn’t bother checking their Maths first. It’s so bad that the Windows calculator in Standard mode says 2+3x4=20. Stick to name brands like Sharp and Casio. They have money invested in the success of their products, so they take more care to make sure it’s correct!

            • Test_Tickles@lemmy.world
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              6 days ago

              I haven’t sent anything to anyone that wasn’t spell checked in more than a decade. So, ya it’s going to be a weird future where you just choose the comment you want to respond to and AI fills it out for you.