Can we say "commutative" in this case ?
this post was submitted on 02 Sep 2025
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Yeah stuff like that really ain't it. It works in a few use cases, but is objectively wrong and detracts from understanding the topic properly. That's why I teach percentages as the fractions they are. By the time you learn percentages, you already know multiplying fractions is commutative, so the trick still works, and you also understand why.
that’s why I teach percentages as the fractions they are
What about pi%?
That's pi/100 still. Didn't say it was a rational number, just that it was a fraction. Though I don't see a context where it'd make sense.
For real? I've never though of this. This may actually be useful!
% really just means *1/100 - it doesn't matter where you apply that factor:
6% of 50 = 6% * 50 = 6/100 * 50 = 6*50/100 = 6 * 50/100
Where were you when I failed math 101 4 times?
Thanks!
I was probably on a different continent ^^ Also, the biggest problem explaining math is not making it understandable, but having a motivated learner. Most students that have a bad teacher in school, or are somehow not motivated in school to begin with, will also not be motivated to focus on easier explanations. Technically a basic interest in math should be fostered / encouraged in kids from an early age, and at the latest in elementary school. If that does not work out, many students will have a hard time with it.
You are welcome.
This is blowing my fucking mind like an artillery shell
Yeah, I personally find it a lot easier to compute 13% of 17, rather than 17% of 13.
.2*13=2.6
.03*13=0.39
2.6-0.39=2.21
My brain is maybe a weird place 😂
Same with 375% of 20 rather than 20% of 375.
Damn, it still worked. Holy shit.
The few times I've seen you on Lemmy, it takes me a few seconds to process your username. Today, I had my favorite misreading yet: pronounced Ivana footerall
Thanks, now I can't unsee that, fartographer
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Actually I disagree.
20% is 1/5
100/5=20
10/5=2
5/5=1
3*20=60
7*2=14
1*1=1
60+14+1=75
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This is the coolest trick since I learned about the "quick 20% tip on your tab" method. Take the total bill, move the decimal point one place over to the left, then multiply it by 2 to get 20% gratuity. I will sometimes round down on the change to make it closer to 18%. Also I only really need to do this when I'm drunk and can't maths.
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x/100 * y = x * 1/100 * y = x * y/100
I never would have thought of it myself and still feel like I should have thought of it myself.
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maths is the same in both case but I get it, for small numbers this is useful
Most of the people explaining this still make it more complicated than it needs to be, imo.
I just think the symbol "%" algebraically means 0.01
This is great. I won't remember it when I will need it.
Today I learned, thank you wise panzer
Wise panzer of the lake. There are other wise panzers, but they are malevolent, untrustworthy.
Legitimately new knowledge for me that will literally make my work easier. Wish I could give you more than 100% of 1 upvote, OP!
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commutable...
I'm gonna track down all my HS math teachers and punch each and every one of them in the mouth.
Huh. Learning a fun and cool math trick was not on the list of expected outcomes for today, but I'll take it!
Surprised how many people don’t know this. I suspect it is because people forget that percent literally means per 100 or /100 and the of is standing in for multiplication. So 6% of 50 is 6/100 * 50 or 6 * 50 * 1/100
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Yes, 47% of 47 is certainly much easier to determine when you look at it as 47% of 47! Genius!
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
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