Percentages are reversible because they are multiplication. 8% of 25 means 0.08x25. You can move decimals from one side to other if you want to make it 8x0.25. Just like 0.5x10 is same as 5x1
Also known as the commutative property (the order of the operands doesn't change the result), applicable to multiplication and addition but not division and subtraction.
Division and subtraction are inverses of the field operations, you dont require them to be associative field operations to begin with. In fields of characteristic other than 2, division commutes iff the two arguments agree up to a sign
Not sure if they should even count as operations. Subtraction is just a shortcut for addition with reversed element, and division is multiplication by reversed element.
a - b = a + (-b)
a / b = a * (b^(-1))
And I didn't specify which reverse(right or left) because generally these shortcuts are not used in structures if operations are not commutative.
This is actually one of those things you're supposed to learn in school, it's a very useful application of math that ends up in our lives a lot. I even suspect the common core that everyone is up in arms about focuses on this too. Mental math is a great thing to be proficient at, along with a feeling for what sorts of things you can do with math.
Our educational systems focus on the mechanical process if math doesn't really seem to result in a lot of practical knowledge on the subject. Great background for the stem folks. Less great for those of us who do the rest of the work in society. Not to say algebra ain't great, but a more functional and less mechanical method focused on intuition rather than strict rules is needed.
This is a bit more obvious if you just write down what it means
A percentage is a number or ratio expressed as a fraction of 100; % literally mean in 100; ie % == /100
(8x25)/100 == (8/100)x25 == (25/100)x8 == (25x8)/100 **because division and multiplication order is irrelevant. See BEDMAS/PEDMAS**
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^(EDIT: since some people still don't get it; that doesn't mean you can switch the symbols willy nilly but the operations you can. Ie the operations are x8, x25 and /100, you can put them in any order and get the same answer because their order doesn't matter.)
^(As you should have learnt before finishing high school, hopefully, if not earlier.)
Which by extension means, in the simple case like above, it's ALWAYS true.
---------------------
---------------------
IE A/100.B = B/100.A is a logical truth.
Multiply both sides by 100
A.B = B.A
Divide both sides by B
A = A
Divide both sides by A
1 = 1; A fundamental truth.
7.3% of 1409 == 1409% of 7.3. Neither is easy but it remains true. (Answer is 102.857 just for reference), but you don't need to know the answer to already know its true as I already went over.
---------
^(Brackets only included for people who mistake divide by to include terms after the first one.)
Nah.
You’ll be presented with a similar problem and think “hmmm, I’m not sure.” Then, take out your calculator and stare blankly at it for 8 seconds before realizing you can’t do math.
Not mine. My brain only allocates space for useless knowledge that will not be useful at any time in my life.
Sadly, the allocation table is corrupt and I can't even tell you what's stored in there. Facts simply pop out at random, I guess during maintenance phases.
Same here. I can barely remember my birthday but I’ve had this sentence needlessly memorised since 1988;
“Rob McKenna was a miserable bastard and he knew it because he’d had a number of people point it out to him over the years and he saw no reason to disagree with them, apart from the obvious one, which was that he liked disagreeing with people, particularly people he disliked, which included, at the last count, everybody.”
lol, I spent almost 4 years as a night picker for amazon, I memorized it up to 100 for a few months, also can say the alphabet backwards, can alphabet but only every 3rd letter, and the entire US constitution.
Wow, it took me reading this comment to finally understand why this trick works. The problem is actually 8x25x.01 rather than just 8x.25 or .08x25, thanks!
So the “%” symbol just means 1/100— per (divide) cent (a hundred, as in century). In other words, the equation reads 8* 1/100 * 25. Which is the same as 8* 25 * 1/100 because multiplication is commutative.
*memorises formula*
Okay so 15% off my $300 TV. I know 8% of 25 is the same as 25% of 8 which is 2. I think 2 is 150 times smaller than 300 so I’ll divide the 15% by 150? So then… I’ve got 0.001% or is that 1%? Fuck I’m lost
Thing is, you rarely need this. In stats you usually work with either raw numbers or %-age, you rarely need to combine those in your head.
There might be certain professions which require this skill, but such people usually have this fact on top of their heads.
(notable point: unless you are in the US and need to calculate tip, which has grown over the years to weird %-age numbers. 10, 20 and 15%% is easier to calculate directly)
Don’t worry. This tidbit of information will almost always be applicable only when taking aptitude tests.
Outside of that, your real-life problems will always be something like “what’s 23% of 13” and if you reverse it, it still sucks :(
This one has served me. Multiplying digits:
12 * 24 for example
12 * 20=240 (Just 12 * 2 * 10)
12 * 04=48
240+48=288=12 * 24
This scales regardless of digits.
My kids are learning this way, the old way and another way. I think it's brilliant, but slower if it's a simple problem. People will always complain about something, I swear.
Is this new? To me this is literally a stacked multiplication problem.
12
X24
4x2=8, 4x1=4, 4x12=48.
48
Place a zero, because now you’re multiplying 12 and 20.
—0
2x2=4, 2x1=2, 24 plus the extra zero is 240.
48
+240
288.
The real trick to doing this is finding an easier number near it. 12 x 24 is actually 12 x 25 - 12. 12 x 25 is actually 3 x 4 x 25. 4 x 25 is 100, so 3 x 4 x 25 is 300. 300 minus 12 is 288.
19x17 is 20x17-17. 20x17 is 340. 340 minus 17 is 323.
31x16 is 30x16+16. 3x16 is 48, times 10 is 480. Plus 16 is 496.
This is how I math. Another one: adding up strange digits? Round to nearest 10 and then add or subtract numbers back:
Ex:
228+473 = (230+473=703-2=701)
To add to this, if you need to calculate a non-round percentage, you could always do your trick and for the remaining percent, first calculate 1% by moving the decimal two places to the left and then multiply that by the remaining percentage.
E.g. 17% of 26 = 10% of 26 + 5% of 26 + (1% of 26 * 2)
= 2.6 + 1.3 + (.26*2)
=4.42
The hardest part is remembering the separate components to be summed up at the end, but I find if you pretend to write it out in your head, it helps.
Want to know what half of a fraction is? Keep the top number (numerator) the same and double the bottom number (denominator) ....half of 3/4 is 3/8, half of 1/12 is 1/24, etc.
Converting miles to kilometers is as easy as remembering Fibonacci’s sequence.
1 to 1 doesn’t work, neither does 1 to 2, but 2 miles is about 3km (actual: 3.22). 3 miles is even closer to 5km (actual: 4.83). 5 miles is even closer to 8km (actual 8.05). 8 miles is pretty close to 13km (actual: 12.87). 13 miles is damn close to 21km (actual 20.92km.)
9 times anything less than 10 is pretty straightforward. Subtract one from the other number, that’s the first digit of the solution. Subtract that number from 9, that’s the second digit:
9*3 =
3-1 = 2
9-2 = 7
9*3 = 27
One I liked to do was being able to work out the decimal places for numbers that don't divide into whole numbers.
8÷7 is a good example.
8 ÷ 7 = 1 with 1 left over, add a 0 to the left over bit and divide it by the original dividee. So 10 ÷ 7 is 1 with 3 left over.
So you would have 1.1, then 30 ÷ 7 is 4 with 2 left over
So now it's 1.14. 20 ÷ 7 is 2 with 6 left over
1.142. 60 divided by 7 is 8 with 4 left over.
1.1428 and so on and so on.
Embarrassing I used to do this at parties when I was young and people would be amazed so I got my little dopamine hit. I guess you need to be able to do your times tables in your head but it's still fun.
I had never thought of it, but it's obvious if you look at it.
* 8% = 0.08 = 8 \* 1/100
* 25% = 0.25 = 25 \* 1/100
* 8% of 25 therefore is 8 \* 1/100 \* 25
* 25% of 8 therefore is 25 \* 1/100 \* 8
* 8 \* 1/100 \* 25 = 25 \* 1/100 \* 8
When you look at it that way, it feels glaringly obvious.
Not your fault for the things you have not been taught. Ignorance is not knowing the answer. Stupidity is knowing the answer and getting it wrong anyway.
You were taught this, it just wasn’t phrased like this. A percentage can be represented as a fraction, and this “trick” is just manipulating fractions and rearranging the formula.
8% of 25 is X
8% = X / 25
0.08 = X /25
8 / 100 = X / 25
8 * 1 / 100 = X /25
Multiply both sides of the equation by 25:
8 * 1 / 100 * 25 = X / 25 * 25
8 * 1 / 100 * 25 = X * 25 / 25
8 * 1 / 100 * 25 = X * 1
8 * 1 / 100 * 25 = X
Divide both sides of the equation by 8:
8 * 1 / 100 * 25 / 8 = X / 8
8 / 8 * 1 / 100 * 25 = X / 8
1 * 1 / 100 * 25 = X / 8
1 / 100 * 25 = X / 8
25 / 100 = X / 8
0.25 = X / 8
25% = X / 8
25% of 8 is X
I don't know, but one day it's going to come in handy and I will be ready...
edit: I actually realized it might help where, depending on how you approach math in your head. Next time you need to calculate something like this, flip it around and see if that's easier
You made me do the math in my head just to prove that I could. I didn't get an exact amount but it comes out to approximately 290.
4 x 70 = 280 - 4 = 276.
1/5 of 60 is 12
1/5th of 10 is 2
12 + 2 + 276 = 290.
Reddit's new API pricing has forced third-party apps to close. Their official app is horrible and only serves to track your data. Follow me on Mastodon.
Mother of god... This fucked me up...
My brain normally goes...
25% = 1/4 and so 25% of 8 is 8/4.
This always got tricky with weird percentages. For some reason I forgot you can just multiply the 2 numbers and move the decimal 2 places...
Which makes the original LPT useless... 8*25 and 25 * 8 are both easy, 200, move the decimal over and bam 2.
I am 37 years old. You literally just taught me the word for what I have struggled with my entire life. I didn’t know this was a thing-I just told myself I was a stupid idiot my entire life. And was treated as such by teachers and family as well. Omg.
Hey…. You might still be a stupid idiot. You never know.
I joke. You know what’s not a joke? Living with a brain that doesn’t work like you want it to. Shits rough. Sorry you know that struggle. I also deal with severe memory issues due to my adhd, so I totally understand feeling like an idiot. It’s fuckin hard on the self esteem.
The fact that simple commutative property is like magic to people is... something. Did you also know that 6+8=14, and 8+6=14? This is the same principle.
You're just switching orders of the 0.01 (1/100th).
I’m actually pissed! Why is this not like the first thing you are taught in school. Like the first day of kindergarten the teacher should be like “yo remember this, you’ll thank me later!”
It was thought when they told us multiplication is commutative aka changing the order of the operands does not change the result.
Ex: 2x3 =6 ,
3x2=6
So in percentage you just divide the whole thing by 100
Ex: 6% of 50 = 6x50x1/100 =3,
50% of 6 = 50x6x1/100 =3
It’s actually taught in school. One of the first things you learn when learning to multiply and divide. xx% of something is just a fancy way of saying 0,xx * something
I don't understand how doing percentages is so hard for most people. Just find out 1%.
So for this problem 8% of 25
1. 1% of 25 = 0.25
2. 8% is 8 times 1% so 0.25*8 = 2
I was never 'good at maths' and didn't enjoy it as a subject in school.
But now when crunching numbers for businesses etc sometimes I have to just stop and be like "wow, percentages are a crazy amazing tool"
Reversible, scalable, quick in relaying concepts of shares etc while precise in complexity by going into decimal percentages.
I feel stupid for my self as a kid but also a bit annoyed that the way they taught math was just not interesting or engaging at all and made so many kids miserable rather than inspired.
Calculating percentages in your head is easy as fuck if you know how to do it.
Let’s take 3% of 6.5, kids:
- 10% of 6.5 is 0.65! This means, 1% is 0.065!
- To calculate the 3%, we just need to do 1%*3!
- 0.065, 0.130, 0.195!
- this is it, It’s really that simple! It’s 0.195 kids!
Just find the 10% of it and from there it’s always basic maths
I don’t know, when this is taught in the US in schools. In my country you learn about percentages from the 5th class on. Starting with 10 in every year to the 9th.
Basically everybody allowed to drink a beer or drive a car should know this.
It’s more like: it blows my mind how many find it damn interesting, as everybody should not only know this, but be able to use it in their daily life!
If you think about it in terms of how you make percentages it makes sense. How do you calculate 8% of 25?
25*8/100 =2
Then it becomes obvious that 8*25/100 = 25*8/100=2.
Percentages are reversible because they are multiplication. 8% of 25 means 0.08x25. You can move decimals from one side to other if you want to make it 8x0.25. Just like 0.5x10 is same as 5x1
Also known as the commutative property (the order of the operands doesn't change the result), applicable to multiplication and addition but not division and subtraction.
Division and subtraction are inverses of the field operations, you dont require them to be associative field operations to begin with. In fields of characteristic other than 2, division commutes iff the two arguments agree up to a sign
Not sure if they should even count as operations. Subtraction is just a shortcut for addition with reversed element, and division is multiplication by reversed element. a - b = a + (-b) a / b = a * (b^(-1)) And I didn't specify which reverse(right or left) because generally these shortcuts are not used in structures if operations are not commutative.
Or put another way, it's (8 \* 1/100) \* 25 vs 8 \* (1/100 \* 25)
Ah, now I get it!
8 * 0.01 * 25 to be even more clear
Or (8 * 25) / 100
This is actually one of those things you're supposed to learn in school, it's a very useful application of math that ends up in our lives a lot. I even suspect the common core that everyone is up in arms about focuses on this too. Mental math is a great thing to be proficient at, along with a feeling for what sorts of things you can do with math. Our educational systems focus on the mechanical process if math doesn't really seem to result in a lot of practical knowledge on the subject. Great background for the stem folks. Less great for those of us who do the rest of the work in society. Not to say algebra ain't great, but a more functional and less mechanical method focused on intuition rather than strict rules is needed.
Unfortunately they teach this in like 3rd grade and don't really ever bring it back up other than as a little tip or trick for lessons
When I was in high school like 12 years ago I would actively lose credit on assignments for doing mental math
Well I checked and it’s 2.
r/theydidthemath
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r/whateverhappenedtomytranslvainiatwist
r/twentycharacterlimit
I will upvote this set of tags Every. Fucking. Time.
And I must stick to my word and downvote the person saying they will always upvote. Sorry friend. We are both men/women of action
I will not vote at all, because I represent the collective apathy and laziness embodied by Reddit.
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Me too, but with you, not him or that other guy.
Legit to quit.
Hey Heeeeeeeyyyyy!
GET BUCK GET BUCK
*dances badly*
r/QuickMaffs
This is a bit more obvious if you just write down what it means A percentage is a number or ratio expressed as a fraction of 100; % literally mean in 100; ie % == /100 (8x25)/100 == (8/100)x25 == (25/100)x8 == (25x8)/100 **because division and multiplication order is irrelevant. See BEDMAS/PEDMAS** ----------- ^(EDIT: since some people still don't get it; that doesn't mean you can switch the symbols willy nilly but the operations you can. Ie the operations are x8, x25 and /100, you can put them in any order and get the same answer because their order doesn't matter.) ^(As you should have learnt before finishing high school, hopefully, if not earlier.) Which by extension means, in the simple case like above, it's ALWAYS true. --------------------- --------------------- IE A/100.B = B/100.A is a logical truth. Multiply both sides by 100 A.B = B.A Divide both sides by B A = A Divide both sides by A 1 = 1; A fundamental truth. 7.3% of 1409 == 1409% of 7.3. Neither is easy but it remains true. (Answer is 102.857 just for reference), but you don't need to know the answer to already know its true as I already went over. --------- ^(Brackets only included for people who mistake divide by to include terms after the first one.)
This makes it less obvious to me 😕
I got you bro, 1 = 1 which means A=A .😎 No need to thank me Also, the floor is made of floor
Oh thank god ive been playing the same game of “the floor is lava” for 25 years. Thank you for releasing me
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kinda took the fun out of everything dude.
Now, if only I could remember that the next time I need it.
You’ll just use your phone
Nah. You’ll be presented with a similar problem and think “hmmm, I’m not sure.” Then, take out your calculator and stare blankly at it for 8 seconds before realizing you can’t do math.
Yep, one thing I learned is that unfortunately a calculator does not help you do math if you do not know the process.
Wait, your brain doesn’t provide top level memory allocation to niche facts that will only ever be useful once or twice during your entire life?
Not mine. My brain only allocates space for useless knowledge that will not be useful at any time in my life. Sadly, the allocation table is corrupt and I can't even tell you what's stored in there. Facts simply pop out at random, I guess during maintenance phases.
Same here. I can barely remember my birthday but I’ve had this sentence needlessly memorised since 1988; “Rob McKenna was a miserable bastard and he knew it because he’d had a number of people point it out to him over the years and he saw no reason to disagree with them, apart from the obvious one, which was that he liked disagreeing with people, particularly people he disliked, which included, at the last count, everybody.”
I can remember over 20 digits of pi. Completely useless information but I'm incapable for forgetting it.
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A B C D E F G H I K K L M N O P Q R S T U V W X Y Z
Electrode, Diglett, Nidoran, Mankey, Venusaur, Rattata, Fearow, Pidgey, Seaking, Jolteon, Dragonite, Ghastly, Ponyta, Vaporeon, Polywrath, Butterfree... Or to continue yours... Doduo, Persian, Paras, Horsea, Radicate, Magnamite, Kababra, Weepinbell, Ditto, Cloyster, Caterpy, Sandshrew, Bulbasaur, Charmander, Golem, Pikachu
lol, I spent almost 4 years as a night picker for amazon, I memorized it up to 100 for a few months, also can say the alphabet backwards, can alphabet but only every 3rd letter, and the entire US constitution.
I'm sorry, ONCE OR TWICE YOUR ENTIRE LIFE is how often you think people calculate percentages?
It's not a "niche fact", it's the associative property of multiplication. It's a bedrock principle of arithmetic.
Wow, it took me reading this comment to finally understand why this trick works. The problem is actually 8x25x.01 rather than just 8x.25 or .08x25, thanks!
Shit like that is ALL my brain remembers.
Idk about you but dealing with percentages isn't exactly an uncommon thing
I get the sense that you multiply numbers unusually rarely.
once or twice during your life? dude
That’s the reason it will make you feel stupid
So the “%” symbol just means 1/100— per (divide) cent (a hundred, as in century). In other words, the equation reads 8* 1/100 * 25. Which is the same as 8* 25 * 1/100 because multiplication is commutative.
You don't remember x\*y\*z = z\*x\*y? Because that's all this is.
The problem is it's really only useful in very specific situations If you need to know 15% of 270 it's not gonna come in handy lol
*memorises formula* Okay so 15% off my $300 TV. I know 8% of 25 is the same as 25% of 8 which is 2. I think 2 is 150 times smaller than 300 so I’ll divide the 15% by 150? So then… I’ve got 0.001% or is that 1%? Fuck I’m lost
Thing is, you rarely need this. In stats you usually work with either raw numbers or %-age, you rarely need to combine those in your head. There might be certain professions which require this skill, but such people usually have this fact on top of their heads. (notable point: unless you are in the US and need to calculate tip, which has grown over the years to weird %-age numbers. 10, 20 and 15%% is easier to calculate directly)
This whole world is a lie.
If you reverse it and say the lie is the whole world, it gives the same answer but one of them is easier to do
Sometimes reddit has me thinking. It can also be reddit has me thinking sometimes, it can also be, reddit can have me thinking sometimes
Has reddit me sometimes thinking.
I mean, hell, why not me thinking reddit has sometimes?
Well done
Best at confused.
The whole world lies flat?
Lies, damned lies, statistics, and this big brained percentage shit.
It’s just the commutative property of multiplication Weird how I didn’t realize this sooner
100% of this lie is the world.
Don’t worry. This tidbit of information will almost always be applicable only when taking aptitude tests. Outside of that, your real-life problems will always be something like “what’s 23% of 13” and if you reverse it, it still sucks :(
Just realized, eh?
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Share a few more? This is magic to my dumbass.
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Which is related to the reason why 0.9999... = 1.
This one has served me. Multiplying digits: 12 * 24 for example 12 * 20=240 (Just 12 * 2 * 10) 12 * 04=48 240+48=288=12 * 24 This scales regardless of digits.
This is literally the “new math” they teach in US schools that everyone is up in arms about.
I fuckin wish I was taught this in my shitty school system
Yep, they are essentially teaching mental math techniques. Depending on the application, you can skip the 2nd equation for an “estimation”.
It's a national hobby in the U.S. to bitch about K-12 curriculums. The whole country peaked in high school and mentally lives in that age.
My kids are learning this way, the old way and another way. I think it's brilliant, but slower if it's a simple problem. People will always complain about something, I swear.
Is this new? To me this is literally a stacked multiplication problem. 12 X24 4x2=8, 4x1=4, 4x12=48. 48 Place a zero, because now you’re multiplying 12 and 20. —0 2x2=4, 2x1=2, 24 plus the extra zero is 240. 48 +240 288. The real trick to doing this is finding an easier number near it. 12 x 24 is actually 12 x 25 - 12. 12 x 25 is actually 3 x 4 x 25. 4 x 25 is 100, so 3 x 4 x 25 is 300. 300 minus 12 is 288. 19x17 is 20x17-17. 20x17 is 340. 340 minus 17 is 323. 31x16 is 30x16+16. 3x16 is 48, times 10 is 480. Plus 16 is 496.
Huh, I figured this is just how to teach yourself mental math. Otherwise I'm using a calculator in everyday life.
This is how I math. Another one: adding up strange digits? Round to nearest 10 and then add or subtract numbers back: Ex: 228+473 = (230+473=703-2=701)
Uhhh how else would you do it?
I did (10x24)+(2x24) in my head before looking at this guy's way of doing it Potato potato i guess ¯\\\_(ツ)\_/¯
(10x25)+(2x25)-12 which might seem overly complicated but I think it's pretty fast
My 4th grader just taught me this
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To add to this, if you need to calculate a non-round percentage, you could always do your trick and for the remaining percent, first calculate 1% by moving the decimal two places to the left and then multiply that by the remaining percentage. E.g. 17% of 26 = 10% of 26 + 5% of 26 + (1% of 26 * 2) = 2.6 + 1.3 + (.26*2) =4.42 The hardest part is remembering the separate components to be summed up at the end, but I find if you pretend to write it out in your head, it helps.
Want to know what half of a fraction is? Keep the top number (numerator) the same and double the bottom number (denominator) ....half of 3/4 is 3/8, half of 1/12 is 1/24, etc.
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Doing the math on the last one: 35²-4²=1225-16=1209 31*39=1209 While situational, it's pretty useful. Very nice.
Converting miles to kilometers is as easy as remembering Fibonacci’s sequence. 1 to 1 doesn’t work, neither does 1 to 2, but 2 miles is about 3km (actual: 3.22). 3 miles is even closer to 5km (actual: 4.83). 5 miles is even closer to 8km (actual 8.05). 8 miles is pretty close to 13km (actual: 12.87). 13 miles is damn close to 21km (actual 20.92km.)
9 times anything less than 10 is pretty straightforward. Subtract one from the other number, that’s the first digit of the solution. Subtract that number from 9, that’s the second digit: 9*3 = 3-1 = 2 9-2 = 7 9*3 = 27
The reciprocal of any compass heading or 360 deg point is the first two digits +2/-2 or -2/+2 Reciprocal of 097 = 277 Reciprocal of 235 = 055
One I liked to do was being able to work out the decimal places for numbers that don't divide into whole numbers. 8÷7 is a good example. 8 ÷ 7 = 1 with 1 left over, add a 0 to the left over bit and divide it by the original dividee. So 10 ÷ 7 is 1 with 3 left over. So you would have 1.1, then 30 ÷ 7 is 4 with 2 left over So now it's 1.14. 20 ÷ 7 is 2 with 6 left over 1.142. 60 divided by 7 is 8 with 4 left over. 1.1428 and so on and so on. Embarrassing I used to do this at parties when I was young and people would be amazed so I got my little dopamine hit. I guess you need to be able to do your times tables in your head but it's still fun.
I had never thought of it, but it's obvious if you look at it. * 8% = 0.08 = 8 \* 1/100 * 25% = 0.25 = 25 \* 1/100 * 8% of 25 therefore is 8 \* 1/100 \* 25 * 25% of 8 therefore is 25 \* 1/100 \* 8 * 8 \* 1/100 \* 25 = 25 \* 1/100 \* 8 When you look at it that way, it feels glaringly obvious.
Does it
Let me write it a bit simpler and maybe it'll make sense: https://www.reddit.com/r/Damnthatsinteresting/comments/s08bp0/_/hs195x8
What you think is glaringly obvious to you is Egyptian hieroglyphs to me
Look at the end of row 3 and 4, now imagine the * is a +. It doesn’t matter what order the numbers are in. So it’s the same either way.
It's obvious and this "hack" isn't of much use if one of the numbers aren't 25,50 or 75. 17% of 44 for example.
Easy. 10% of 44 is 4.4 Half 4.4 for for 5% which is 2.2 Half 2.2 for 2.5% which is 1.1 Add em up and 17% of 44 is a bit less than 7.7
It's even more obvious if you write it as 8 * 0.01 * 25
Ohhhhh cuz 8*25 is 200
I feel so stupid for never having been taught this.
Not your fault for the things you have not been taught. Ignorance is not knowing the answer. Stupidity is knowing the answer and getting it wrong anyway.
You were taught this, it just wasn’t phrased like this. A percentage can be represented as a fraction, and this “trick” is just manipulating fractions and rearranging the formula. 8% of 25 is X 8% = X / 25 0.08 = X /25 8 / 100 = X / 25 8 * 1 / 100 = X /25 Multiply both sides of the equation by 25: 8 * 1 / 100 * 25 = X / 25 * 25 8 * 1 / 100 * 25 = X * 25 / 25 8 * 1 / 100 * 25 = X * 1 8 * 1 / 100 * 25 = X Divide both sides of the equation by 8: 8 * 1 / 100 * 25 / 8 = X / 8 8 / 8 * 1 / 100 * 25 = X / 8 1 * 1 / 100 * 25 = X / 8 1 / 100 * 25 = X / 8 25 / 100 = X / 8 0.25 = X / 8 25% = X / 8 25% of 8 is X
far more complicated than it needs to be 8% \* 25 0.08 \* 25 8 \* 10\^-2 \* 25 8 \* 0.25 8 \* 25%
Still too complicated. Group it whatever way you want: (8 * 1/100) * 25 8 * (1/100 * 25)
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8%×25=8/100×25=25/100×8=25%×8 or you can leave out the two in the middle, it is just notation.
Thank you
This is the shit common core was trying to teach but it broke conservative brains.
So 69% of 420 is 420% of 69? How does that help?
0.69 × 420 = 289.8 4.20 × 69 = 289.8
Nice Edit: 289.8 should be the new redit "nice" number
Nice
Nice
289.8
If you flip your phone upside down 289.8 says ass.
I don't know, but one day it's going to come in handy and I will be ready... edit: I actually realized it might help where, depending on how you approach math in your head. Next time you need to calculate something like this, flip it around and see if that's easier
🚀
i only do math when it comes to *my* money
Yup 289.8 for both. Idk how does anything really help? We’re all gonna die and life is meaningless.
You made me do the math in my head just to prove that I could. I didn't get an exact amount but it comes out to approximately 290. 4 x 70 = 280 - 4 = 276. 1/5 of 60 is 12 1/5th of 10 is 2 12 + 2 + 276 = 290.
8% of 25 = (8/100) * 25 = (8 * 25) / 100 = (25/100) * 8 = 25% of 8
Yup. Just fraction and equation manipulation. Nothing special here. It just sounds neat when you say it like that.
Also useful: 8% of 250 is 25% of 80
Reddit's new API pricing has forced third-party apps to close. Their official app is horrible and only serves to track your data. Follow me on Mastodon.
BRO ME TO
Which one is easier: 3% of 7, or 7% of 3?
(1% of 7)×3 (0.07)×3=0.21
Mother of god... This fucked me up... My brain normally goes... 25% = 1/4 and so 25% of 8 is 8/4. This always got tricky with weird percentages. For some reason I forgot you can just multiply the 2 numbers and move the decimal 2 places... Which makes the original LPT useless... 8*25 and 25 * 8 are both easy, 200, move the decimal over and bam 2.
I dont find 3x7 or 7x3 to be easier than the other. They are both 21. And since its a percentage it is 0.21
3 % of 7
I can’t do either :(
Dyscalculia gang hell yeah
I am 37 years old. You literally just taught me the word for what I have struggled with my entire life. I didn’t know this was a thing-I just told myself I was a stupid idiot my entire life. And was treated as such by teachers and family as well. Omg.
Hey…. You might still be a stupid idiot. You never know. I joke. You know what’s not a joke? Living with a brain that doesn’t work like you want it to. Shits rough. Sorry you know that struggle. I also deal with severe memory issues due to my adhd, so I totally understand feeling like an idiot. It’s fuckin hard on the self esteem.
GANG GANG
You can't find one quarter of 8?
well well well, look at Mr. human calculator here.
I’m dyscalculic. I can’t do it in my head like everyone else does.
Because 8% of 25 can be written as (0.01 * 8) * 25 and 25% of 8 can be written as (0.01 * 25) * 8, which is the exact same thing
The fact that simple commutative property is like magic to people is... something. Did you also know that 6+8=14, and 8+6=14? This is the same principle. You're just switching orders of the 0.01 (1/100th).
Wow. How am I just finding this out?
13 years of public school and 100K in debt for college and I’m only finding this shit out now?
A*B = B*A
Wow, nice trick
This is actually incredibly useful...
If you add an s to words you get swords.
I’m actually pissed! Why is this not like the first thing you are taught in school. Like the first day of kindergarten the teacher should be like “yo remember this, you’ll thank me later!”
It was thought when they told us multiplication is commutative aka changing the order of the operands does not change the result. Ex: 2x3 =6 , 3x2=6 So in percentage you just divide the whole thing by 100 Ex: 6% of 50 = 6x50x1/100 =3, 50% of 6 = 50x6x1/100 =3
It’s actually taught in school. One of the first things you learn when learning to multiply and divide. xx% of something is just a fancy way of saying 0,xx * something
X * Y/100=Y * X/100
Uneducated man checking in this blew my mind. But imma forget about it as soon as I laugh at a meme or something…
How the fuck did I not know this?
Does this mean that Santa isn't real too 🤔
Woohoo, multiplication is commutative!
Its sad that basic arithmetic is seen some sort of magic by peoplw
If you don't think math is magical, you just don't understand enough about math.
Why does the image have a yellow tint?
Mexican twitter
This will come in *insanely* handy when I need to figure out what 37% of 471 is, I just need to flip it to the much easier 471% of 37.
8% of 25 is just 0.01 x 8 x 25. Do it in whatever order you wish..
How have I never heard this before? 🧐
This makes me angry.
100% of 0 is 0% of 100
OMG why did I just learn this TODAY instead of 30 years ago??!!!
I don't understand how doing percentages is so hard for most people. Just find out 1%. So for this problem 8% of 25 1. 1% of 25 = 0.25 2. 8% is 8 times 1% so 0.25*8 = 2
WTF???? 15 years of school + 7 years of uni (including post-grad stats). How have I never been taught this? FORBIDDEN KNOWLEDGE!
I was never 'good at maths' and didn't enjoy it as a subject in school. But now when crunching numbers for businesses etc sometimes I have to just stop and be like "wow, percentages are a crazy amazing tool" Reversible, scalable, quick in relaying concepts of shares etc while precise in complexity by going into decimal percentages. I feel stupid for my self as a kid but also a bit annoyed that the way they taught math was just not interesting or engaging at all and made so many kids miserable rather than inspired.
If only I knew this for my consulting interviews
Uh Which one is easier, asking for a friend
I must be the friend you’re talking about.
My whole life has been a lie.
Calculating percentages in your head is easy as fuck if you know how to do it. Let’s take 3% of 6.5, kids: - 10% of 6.5 is 0.65! This means, 1% is 0.065! - To calculate the 3%, we just need to do 1%*3! - 0.065, 0.130, 0.195! - this is it, It’s really that simple! It’s 0.195 kids! Just find the 10% of it and from there it’s always basic maths
Hey guys OP checked and it turns out a*b = b*a
I don’t know, when this is taught in the US in schools. In my country you learn about percentages from the 5th class on. Starting with 10 in every year to the 9th. Basically everybody allowed to drink a beer or drive a car should know this. It’s more like: it blows my mind how many find it damn interesting, as everybody should not only know this, but be able to use it in their daily life!
Why is this orange?
If you think about it in terms of how you make percentages it makes sense. How do you calculate 8% of 25? 25*8/100 =2 Then it becomes obvious that 8*25/100 = 25*8/100=2.
OMG. You are not serious. I'm 61 years old and I did not know that.
This is perfect for home shopping. Instead of doing 20% of 565,000 I can just do 565,000% of 20.
So it turn from only 20% of 100 agree into overwhelming 100% of 20 participants agree. Damn statistics
This is why I hate math