Maths

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.
- Same with 375% of 20 rather than 20% of 375.
- .2*13=2.6
  .03*13=0.39
  2.6-0.39=2.21
  My brain is maybe a weird place 😂
I guess it's easy to miss that m% just means ×m÷100
6% of 50 means 50 × 6 ÷ 100, and because multiplication and division have the same order of operations you can switch them around. so it is also equal to 6 × 50 ÷ 100, in which you can simplify 50 ÷ 100 into 1 ÷ 2, but you could always do that: 50 × 6 ÷ 100 = 1 × 6 ÷ 2.
this "shortcut" however is of extremely limited use. basically for taking a percentage of anything other than things that can very easily divide or multiply 100 like 50 in this example or maybe 10 or 500 it's nearly useless.
It's because percent just means ×0.01 and multiplication can be rearranged

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.

So 37 % of 38 is equivalent to (37 * 38 ) / 100 ? Which I can almost do in my head.
37 * 4 is 148 I think, so 37 * 40 is 1480. Subtract 74 we have 1406. So we have 14.06?
- You're hired
- For a while I’ve been meaning to memorize all the two digit squares but of course I then fail to practice them, so I’m not very far along. But that would help you with this too, not to mention you can start doing some square roots too.
  For quick and dirty I’d probably just go with 37*38 = 40*40 -> 16% which is kinda close to 14% eh?

23% of 53
- 53% of 23, next question
- Pretty close to 1/4 of 52, so like 13-ish, but maybe closer to 12.
  (13 + 0.25 - 0.53 - 0.53, really. If I had to, I might be able to keep that in my head.)
Babagedegaga. Ba.

My dyscalculic ass trying to remember what 50% of 6 is

Probably 5 tbh

This is great. I won't remember it when I will need it.

Just save the meme in the maths folder!
- You clearly don't have gigs of memes.
- You shut your whore mouth

6/100 * 50 = 50/100 * 6
6 * 1/100 * 50 = 50 * 1/100 * 6

- it all equals 3

Legitimately new knowledge for me that will literally make my work easier. Wish I could give you more than 100% of 1 upvote, OP!

I wish someone told me this trick 30 years ago.
1 of 100% upvote. Yeah, it checks out!

650/100 = 506/100 if anyone is curious why this works.

Or, more generally:
Taking X percent of something is the same as multiplying by X/100.
X percent of Y = Y(X/100)=(YX)/100
Y percent of X = X(Y/100)=(XY)/100
(YX)/100=(XY)/100
Percentages are indeed reversible.

I'm gonna track down all my HS math teachers and punch each and every one of them in the mouth.

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.

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

Can we say "commutative" in this case ?

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%?

commutable...

That's because multiplication is commutative

taking a percentage of something essentially means multiplying it with a hundreath of the percentage
6% of 50 essentially means 50 * 0.06
or 50 * 6 * 0.01

and since
50 * 6 * 0.01 = 6 * 50 * 0.01
then of course
50 * 0.06 = 6 * 0.5

And we have the above

I prefer to keep it technically correct yet evil and confusing. 6% being a fancy way to write 0.06 or 6 1/100 means we can take 6 50 1/100 and simplify to 300 1/100 and then represent that as 300%.
- Chat is this real
- Finally a reasonable way to do percentages! Thank you, I'm stealing this
Yeah my brain just sees 5*6, and then I move the decimal. I never understood how people couldn't figure out tips when they wanted 20%.
If you live in the U.S. you do them quite often, multiply by 2. Want 10 multiply by .1... Half that and add it if you want 15. Whatever is easiest at that moment
... in 1 or 2 dimensional number systems, also known as the real (1-dimension) and the complex (2-dimensions) numbers. With quaternions and higher dimensional systems multiplication is not communicative. In fact, the more dimensions you add, another mathematical property is lost.
- ... okay? Yes? Nobody thought otherwise? Do we now have to clarify every statement about algebra by specifying that we're talking about an algebra over the reals or the complex numbers? Or the polynomials or the p-adic integers, whose multiplications are also commutative?
  No one would call these "n-dimensional" number systems either. The algebra for each of these operates in R¹ and R², respectively, but, like, you would describe their algebras as being over an n-dimensional vector space. It's not wrong, but I don't think "two-dimensional number system" is something you'd hear mathematicians say.
  This pedantic aside feels so "I just watched a 3blue1brown video and feel verysmart(TM)" that I don't know what to do with it. It's good to be interested in math, but this ain't it. Everyone knew what they meant.

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
- Why do you have to divide on both sides in your example with 14% of 200?
- 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...

Huh. Learning a fun and cool math trick was not on the list of expected outcomes for today, but I'll take it!

Today I learned, thank you wise panzer

Wise panzer of the lake. There are other wise panzers, but they are malevolent, untrustworthy.

Teaching stats and using percentages now and again, it's not really that useful of a tool most of the time since you aren't usually working with an easy number like 50 (Or 10, 20, 25, etc.).

Usually what I'm doing is breaking it down into manageable parts (factors), so 6% is 5% + 1% which I can usually do in my head regardless of the number (or if 5% hard, work in increments of 1%, which I can multiply by 6).

It's a pretty common strategy to with with factors. Just surprised how many of my students don't know 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

I have been looked at like a wizard saying "oh that's just the amount times 1.2"

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!

Sweet, thanks Panzer of the Lake!

Yeah, now calculate 6% of 36

Edit: Replies itt make me believe that everyone on Lemmy is a chatbot

Bout tree fiddy
6% of 36 is 0.06 * 6². 6³ = 216 so 2.16
1% of 36 is .36, and .36 * 6 = 2.16. I'm a fan of this method most of the time, though the one in the OP is good for some math problems.
36% of 6 is roughly 33.(3)% of 6 which is 2.
3% of 6 is .18 so about 2.18
I usualy get the value of 1% and then multiple that back to original, so:
1% of 36 is 0.36 (just move 2 spaces) and thats times 6 which is 2.16
3.6/2+0.36 = 2.16
(10% of 36 halved, so 5%, plus 1% of 36)

Danke

maths is the same in both case but I get it, for small numbers this is useful

For those who want to dive deeper into the lake and the wisdom of the panzer: https://en.m.wikipedia.org/wiki/Commutative_property

50*.06 = 5061/100 = .5*6

But you're still just multiplying 5*6 and then moving the decimal point around. So don't sweat it.

I'm still doing a rule of threes either way.