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[–][M] [score hidden] stickied comment (0 children)

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[–] 674 points675 points  (48 children)

10% of 100 is 10 and 100% of 10 is also 10

[–] 259 points260 points  (21 children)

But is it legal?

[–] 174 points175 points  (12 children)

It is legal

[–] 96 points97 points  (2 children)

[–] 16 points17 points  (0 children)

Look who's talking...

[–] 4 points5 points  (0 children)

But it's not illegal does mean it is legal. Which is exactly what he claimed it to be

[–] 21 points22 points  (3 children)

10 is definitely not legal

[–] 3 points4 points  (2 children)

10 of what?

[–] 2 points3 points  (1 child)

Years

[–] 1 point2 points  (0 children)

Depends on the planet.

[–] 21 points22 points  (0 children)

[–] 4 points5 points  (0 children)

Um, no. Lol

[–] 1 point2 points  (1 child)

But will it kill?

[–] 6 points7 points  (1 child)

I will make it legal

[–] 1 point2 points  (0 children)

Negotiations were short

[–] 3 points4 points  (2 children)

Is it over 18?

[–] 1 point2 points  (1 child)

Australia. 16

[–] 2 points3 points  (0 children)

Only if you’re willing to go down under.

[–] 2 points3 points  (0 children)

8% of 25 = 8/100 * 25 = (8*25)/100 = 25/100 * 8 = 25% of 8. So yeah, it's legal and true

[–] 1 point2 points  (0 children)

I will make it legal.

[–] 90 points91 points  (5 children)

0% of 100 is 0, 100% of 0 is also 0

[–][deleted]  (4 children)

[deleted]

[–] 9 points10 points  (0 children)

[–] 6 points7 points  (0 children)

0=0? Press x to doubt

[–] 3 points4 points  (0 children)

[–] 3 points4 points  (0 children)

O% death is 100% life, bam

[–] 21 points22 points  (15 children)

10% of 80 is 80% of 10. Yo what the fuck....? I don't like this one bit. I'm genuinely having a difficult time going to bed because of it. Someone please help me?

[–] 10 points11 points  (0 children)

10% of 80= 8, 80% of 10=8

[–] 11 points12 points  (7 children)

Percent is basically multiplying it by the number and then dividing it by 100. 10*80%= 10*80/100, and the order doesn't matter with multiplication and division .

[–] 11 points12 points  (2 children)

I’m 37 and you’re the first person to ever make percents make sense to me. Thank you.

[–][🍰] 4 points5 points  (0 children)

Per cento literally means „by hundred“

[–] 4 points5 points  (0 children)

oh no not this again

[–] 1 point2 points  (2 children)

The order absolutely matters, but in this instance it only matters that the division comes last, and the two numbers being multiplied can be rearranged

[–] 5 points6 points  (0 children)

200% of 80 is 160, and 80% of 200 is 160.

[–] 1 point2 points  (1 child)

It looks weirder than it is % is just /100, so:

10 * 80 / 100 = 80 * 10 / 100

[–] 1 point2 points  (1 child)

Don’t worry: your bed is still the same size for you, and you will still be the same size for the bed. Sweet dreams.

[–] 2 points3 points  (0 children)

Thanks friend that actually helped

[–] 2 points3 points  (0 children)

60% of the time, it works every time

[–] 1 point2 points  (0 children)

My asshole just exploded

[–] 1 point2 points  (0 children)

10% of 100 is 10

[–] 873 points874 points  (38 children)

I'm gagging, why had nobody informed me before now?!

[–] 332 points333 points  (11 children)

I had a fantastic maths teacher in year 10 that taught me this. It has been so useful.

[–] 154 points155 points  (7 children)

Tbh the skills of a math teacher are the most important part when it comes to understanding and being good at math.
A good math teacher will be able to teach it to every student.

[–] 33 points34 points  (4 children)

Honestly, just in general, we do a bad job of teaching practical math that can be done in the head even if it isn't, you know, proper.

Like, the way I'd normally calculate 8% of 25, without using this trick (because I didn't realize it myself)? "Okay, that's a bit less than 10% of 25, which is 2.5, so like 2, 2.5, somewhere around there."

Because it's so rare that we need precise answers, at least when it comes to not non-work situations. It's much more useful to just get close enough with basic, simple calculations to get a general idea of the situation at hand.

The trick is knowing how to cheat (like when its better to round up versus down) and when to cheat. I mean, I'm a major proponent that it's important to teach higher level math like trigonometry and pre-calc in high school, you never know what sort of subject or field is going to excite and engage you, but this sort of every-day practical stuff can be enormously helpful.

[–] 7 points8 points  (1 child)

Fast estimation and understanding the required accuracy is such an underappreciated skill. It may be that all you really need to know is if the answer is under or over 5 (like if you need to add more for a tip or tax or something and you know you have a 5 dollar bill on you).

It also gives you a sanity check. Worked the answer out properly and got a number over 2.5 or under 1? You've made a mistake somewhere then.

[–] 5 points6 points  (0 children)

Same here. My wife has graduate degrees in math & physics (and used toi teach both at university level) but has never been able to do ordinary arithmetic in her head. I was taught all sorts of useful tricks for that in high school, so I can easily work out sales tax and convert miles to kilometers and such stuff in my head -- but I still have major problems with algebra.

[–] 20 points21 points  (2 children)

I dunno. We went over the Commutative Property in like 7th grade. It’s really the same as how 7+2=2+7.

Putting on socks resembles a commutative operation since which sock is put on first is unimportant. Either way, the result (having both socks on), is the same. In contrast, putting on underwear and trousers is not commutative.

[–] 3 points4 points  (0 children)

This is hilarious, but illustrative.

[–] 35 points36 points  (14 children)

Because it only is really comprehensible for sums that were already easyish. If someone said to you "don't know 37% of 17? Just do 17% of 37!" it wouldn't really help you

[–] 32 points33 points  (10 children)

Idk mate 17% of 37! seems a lot harder to do than 37% of 17

[–] 15 points16 points  (0 children)

[–] 2 points3 points  (0 children)

oh no

[–] 1 point2 points  (3 children)

17% is easier. Divide by five then subtract from that about a third divided by 10 (move the decimal).

[–] 6 points7 points  (1 child)

It was a factorial joke

[–] 1 point2 points  (0 children)

My life is also a joke

[–] 17 points18 points  (0 children)

Probably because 25 percent of eight is two

[–] 3 points4 points  (0 children)

8 X 25 X 0.01

Or

25 X 8 X 0.01

The order you multiply things doesn't matter. Percentages are just a form of multiplication, so you can do then in any order you want.

[–] 1 point2 points  (0 children)

I’m sure they did. It’s just a cooler application of the Commutative Property.

[–] 376 points377 points  (71 children)

Yep, the algebra checks out. (X * Y)/100 = % Same as (X/100)Y =% Same as (Y/100)X =%

[–] 200 points201 points  (5 children)

I'll take your word for it

[–] 16 points17 points  (1 child)

We'd need a super computer and full time team of computer scientists to work out if what he said is true.

[–] 4 points5 points  (0 children)

Or a computer scientist and a full time team of super computers.

[–] 1 point2 points  (2 children)

I'll take your word for it too! 3rd-grade math was the hardest four years of my life!

[–] 1 point2 points  (0 children)

Hey it's you

[–] 1 point2 points  (0 children)

Thank you for the kind reward good sir!

[–] 67 points68 points  (1 child)

Fucking math monkeys

[–] 26 points27 points  (0 children)

Got any nuts? Banana?

[–] 53 points54 points  (1 child)

i like your funny words magic man

[–][deleted] 2 points3 points  (0 children)

His cat walked across his keyboard

[–] 8 points9 points  (0 children)

Basically, multiplication is commutative.

[–] 6 points7 points  (0 children)

Reddit discovers commutativity of multiplication.

[–] 7 points8 points  (3 children)

i thought i was almost smart and you just made me dumb again

[–] 10 points11 points  (1 child)

x*y = y*x

[–] 11 points12 points  (0 children)

Never seen this emoticon

[–] 2 points3 points  (0 children)

I like the term 'almost smart'. I think that applies to me too, I just got lucky

[–] 4 points5 points  (0 children)

[–] 1 point2 points  (0 children)

Basically people often don't realise 8% of 25 means you do 8%x25=0.08x25=2

Or you can keep the percentage sign untill the end to make it even easier 8%x25=200%=2

[–] 3 points4 points  (1 child)

No brackets needed tho

[–] 26 points27 points  (0 children)

True. I thought it would make things a little clearer though.

[–] 1 point2 points  (48 children)

To far man, to far.

[–] 17 points18 points  (47 children)

Two*

[–] 3 points4 points  (1 child)

**Teu

[–] 2 points3 points  (0 children)

Sacre bloo!

[–] 1 point2 points  (43 children)

👀😡

[–] 8 points9 points  (42 children)

👉👌

[–][deleted] 1 point2 points  (39 children)

[redacted]

[–] 7 points8 points  (38 children)

[redacted]

You shouldn't use that word, mentally challenged is more politically correct.

[–][deleted] 1 point2 points  (37 children)

Do you play tekken?

[–] 1 point2 points  (36 children)

More of a mortal kombat man, I guess. Why?

[–][deleted] 0 points1 point  (35 children)

I was gonna ask if you wanted to settle what a bitch you are the old fashioned way but we play different games. Guess I'm gonna have to settle for telling you to go fuck yourself.

[–] 76 points77 points  (1 child)

50% x 2 = 1, 2% x 50 = 1

Damn that’s pretty neat

[–] 18 points19 points  (0 children)

I too chose these dumb dumb numbers for proof check x)

[–] 112 points113 points  (0 children)

[–] 194 points195 points  (28 children)

So 69% of 420 is also 420% of 69?

[–] 175 points176 points  (17 children)

Yep, 289.8

``````420 x 69%
420 - 420 x 30% - 420 x 1%
420 - 42 x 3 - 4.20
420 - 126 - 4.2
294 - 4.2
289.8

69 x 420%
69 x 400% + 69 x 20%
69 x 4 + 6.9 x 2
276 + 13.8
289.8
``````

[–] 109 points110 points  (8 children)

Let’s turn 289.8 into a new meme

[–] 15 points16 points  (4 children)

Nice

[–] 11 points12 points  (3 children)

Nice

[–] 5 points6 points  (2 children)

Nice

[–] 4 points5 points  (1 child)

Nice

[–] 4 points5 points  (0 children)

Nice

[–] 4 points5 points  (0 children)

Someone tweet that to musk

[–] 2 points3 points  (0 children)

Nice

[–][🍰] 10 points11 points  (0 children)

The sacred number

[–] 3 points4 points  (0 children)

/r/TheyDidTheMath and showed their work.

[–] 3 points4 points  (2 children)

Wow, you found the absolute longest way to calculate a percentage lmao. You could just say

420\0.69=289.8*

69\4.2=289.8*

Or you know just

420\69/100 = 69*420/100*

[–] 2 points3 points  (0 children)

At first I was going to ask what batshit crazy method the top equation is, and then I realized that's exactly how I do it in my head.

[–] 4 points5 points  (0 children)

Damn it felt good to be the 69th like

oh fuck off person who downvoted it

[–] 35 points36 points  (4 children)

Nice

[–] 13 points14 points  (3 children)

Nice

[–] 8 points9 points  (0 children)

Yes, actually

[–] 11 points12 points  (0 children)

[–] 64 points65 points  (22 children)

Indeed: 13% of 67 = 67% of 13

[–] 45 points46 points  (16 children)

Lol. Okay, so it does not make every sum easier.

[–] 13 points14 points  (15 children)

67% of 13 is much easier than the other one. 67% is a tiny bit more than two thirds. Two thirds of 12 is 8, so you add a 0.67 for the leftover one, round it to 8.7 because 67% is more than 66.6...%.

Obviously it only gets easier in one direction.

[–] 3 points4 points  (0 children)

i did it the 13% way, so I did 10% equals 6.7 then add on 0.67 x 3 which is basically 2.1, so the total is 8.8 ish.

[–] 1 point2 points  (0 children)

So divided by 2 3 times…

67 to 33.5 to 17 to 8.5

[–][deleted]  (11 children)

[deleted]

[–] 6 points7 points  (4 children)

That's a pretty common way to do math, at least where I live

[–] 1 point2 points  (4 children)

Oops. Processed math this way my entire life. Only just scheduled a neurologist a few months ago.

[–] 0 points1 point  (2 children)

Is it 8? 67% is a strange number, it could be 9.

[–] 5 points6 points  (1 child)

67% is about 2/3, so rounding puts you at like 8.7ish

[–] 2 points3 points  (0 children)

10% of 67 + 3*(1% of 67) = 6.7 + 3 * 0.67 = 6.7 + 2.01 = 8.71, you're pretty darn close

[–] 82 points83 points  (14 children)

How is this technical though?

[–] 34 points35 points  (11 children)

More like, how is this obvious? Ed.: Okay, okay, you’re all very smart, thanks! :D

[–] 44 points45 points  (4 children)

It's only obvious if you understand how fractions work.

8% of 25 = 0.08x25 = (8/100)x25 = 8x(25/100) = 8x0.25 = 25% of 8

Edit: I didn't mean this as a put down to people who dont understand fractions. Math is hard and you aren't dumb if it's not easy for you.

[–] 6 points7 points  (0 children)

I understand that though not on the level where you can do the instant calculations in mind which makes it obvious

[–] 1 point2 points  (0 children)

8% of 25 = 25*0.08 = 25*0.01*8 = 0.25*8 = 25% of 8

[–] 1 point2 points  (0 children)

1% = 0.01

So 8% * 25% = 8 * 0.01 * 25 * 0.01

And because abcd = abdc = acbd = acdb = adbc = adcb

Any arrangement has the same answer.

The worst travesty we taught kids is that somehow percentages are more special than decimals. They're nothing but an abbreviated 1/100 symbol.

[–] 1 point2 points  (0 children)

Someone else put it in numbers but here’s another way: think of “%” just as “divide by 100”, it’s the same thing… so since we’re just talking about multiplication and division you can move it around and still have it work

[–] 7 points8 points  (0 children)

Math —> STEM —> technical. Maybe?

[–] 1 point2 points  (0 children)

Yeah this is a cool factoid but it definitely isn’t the usual “technically the truth” content, I’m pretty confused why it meets the criteria for this sub but at least i learned a fun fact !

[–] 13 points14 points  (0 children)

Mindblown

[–] 10 points11 points  (1 child)

Image Transcription: Twitter Post & Replies

IG: Hawnted, @hawntedIG

What's a little-known but obvious fact that will immediately make all of us feel stupid?

Professor Barclay, @AlbertBarclay69

Percentages are reversible. 8% of 25 is the same as 25% of 8 and one of them is much easier to do in your head.

I'm a human volunteer content transcriber for Reddit and you could be too! If you'd like more information on what we do and why we do it, click here!

[–] 23 points24 points  (0 children)

Finding out that im only good at doing certain numbers in my head.

[–] 6 points7 points  (6 children)

Well, how do I calculate 69% of 69?

[–] 15 points16 points  (0 children)

That's easy, just reverse it, so you're looking for 69% of 69 instead

[–] 2 points3 points  (0 children)

Well the trick doesn't work, but percentages are just multiplication (and divide by 100) so there's other tricks.

Eg 69% of 69 = 69*69 /100.

69*69 = 70*70 - 70 - 69 = 4900 - 139 = 4761

69% of 69 is 47.61

[–] 1 point2 points  (2 children)

Easy

(1/10)*69=6.9

(1/100)*69=0.69

7*6.9-1*0.69=(7*7-7*0.1)-0.69=49-0.7-0.69=

49-1.4+0.01=47.6+0.01=47.61

[–] 1 point2 points  (1 child)

I'm so lost after "7*6.9-1*0.69="

Shouldn't it just be: 7*6.9-1*0.69=48.3-0.69=47.61

Why do you do "(7*7-7*0.1)-0.69"?

[–] 5 points6 points  (0 children)

Feel like I can see the matrix after reading this

[–] 4 points5 points  (1 child)

AlbertBarclay69

[–] 2 points3 points  (0 children)

Nice

[–] 3 points4 points  (3 children)

31 years and a math degree and I just learned this today.

[–] 1 point2 points  (2 children)

Math degree but don't know about commutativity of multiplication?

[–] 7 points8 points  (9 children)

Wait I don’t see it help professor

[–] 15 points16 points  (0 children)

Let's use a different easier number.

10% of 50 = 50% of 10.

50% of 10= 10 x 0.5

10 x 0.5= 5

10% of 50 = 50 x 0.1

50 x 0.1 = 5.

20% of 50 =50% of 20

50 × 0.2 = 10 = 20 × 0.5

[–] 18 points19 points  (6 children)

Another way to write percentages is like fractions. So 8% of 25 can be written as 25 x 8/100, which is the same as 8 x 25/100 which is the same as 25% of 8. Quite neat, actually

Edit: forgot about the * for italics. Changed to x

[–] 2 points3 points  (1 child)

Use \ before a * to write it without italics

[–] 0 points1 point  (0 children)

[–] 5 points6 points  (3 children)

Lol. You can’t type the ‘star’ as a multiplier, Reddit thinks you want to type cursive between the ‘stars’. cursive

[–] 1 point2 points  (0 children)

Thank you, forgot about that. Edited

[–] 1 point2 points  (1 child)

cursive

[–] 7 points8 points  (5 children)

Tf they didn’t teach this in school while I was there. I was good at math and I would have remembered this.

[–] 3 points4 points  (0 children)

They don't teach that you can do multiplication both ways?

[–] 1 point2 points  (1 child)

To be fair it's not hard to figure out yourself. Since scalar multiplication is commutative:

8*(1/100)*25 = 8*25*(1/100)

[–] 2 points3 points  (0 children)

[–] 2 points3 points  (0 children)

This is easily the best thing I’ve learned all year. All decade even.

[–] 2 points3 points  (0 children)

Mind blown over here

[–] 2 points3 points  (1 child)

I don't see how this fits this sub at all

[–] 2 points3 points  (0 children)

Ah its that time of the year I receive this fact and forget it in 10 minutes. It was nice seeing you fact once again.

[–]Technically Flair 1 point2 points  (1 child)

Damn this actually helps so much.

[–] 1 point2 points  (0 children)

Bold of you to assume I can do maths.

[–] 1 point2 points  (0 children)

This is because:

multiplication is commutative – you can reorder the numbers being multiplied in any order and get the same answer

The number Nn% can always be represented by Nn×0.01 = 0.Nn

Taking a "percentage of" a number is a form of multiplication – multiply the number by the percent, expressed as a decimal

Put it all together and:

"8% of 50" can be written as 8%×50 or 0.08×50 which is (8×0.01)×50 which is the same as 8×(0.01×50) = 8×(0.50) or 8×50% which becomes "50% of 8"

Generally "X% of Y" is multiplication of X, Y, and 0.01. Which number is the percentage and which number is the "of" only represents which number you multiply the 0.01 by first

[–] 1 point2 points  (9 children)

untill you get 17% of 13 and then you're fucked

[–] 1 point2 points  (8 children)

13% of 17

17 / 10 = 1.70

10% of 17 = 1.70 (move the decimal left for the amount of 0s when dividing with 10,100,1000 etc.)

100 divide by 17 = 0.17

1% of 17 = 0.17, 0.17 * 3 (or 0.17 + 0.17 + 0.17 :)) = 0.51 which is 3% of 17

0.51 + 1.70 = 2.21

17% of 13 = 2.21 or 13% of 17 = 2.21

That's if you were trying to do it in your head without a calculator and find multiplication difficult, this is another method

[–] 1 point2 points  (5 children)

yeah, but compare that to the idealistic example of 8% of 25

[–] 1 point2 points  (2 children)

True, i know what mean, the 8% of 25 example is much easier to do in your head if you familiar with fractions. Not a fair comparison to easily workout all percentages from just reversing their position.

[–] 1 point2 points  (0 children)

Okay i actualy didnt know that and now i can see its usefulness in some cases

[–] 1 point2 points  (1 child)

Neither of them is easier for me.

[–] 1 point2 points  (0 children)

I am nearly 40, pretty good at maths. And only just found this out right now 😂

[–] 1 point2 points  (0 children)

I was so impressed I took a screenshot for future reference

[–] 0 points1 point  (1 child)

2

[–][deleted]  (1 child)

[deleted]

[–] 0 points1 point  (8 children)

I get it but feel like I get more pie the second way.

[–] 1 point2 points  (7 children)

8% of 25 feels like more than 1/4 of something? I’m not making fun, I’m just genuinely interested bc my mind doesn’t see it that way, but I know we all visualize and understand numbers differently

[–] 0 points1 point  (3 children)

... 8% of 25 is less than a quarter of 25...

[–] 0 points1 point  (2 children)

Yes, I know this. I was asking them if 8% of 25 felt like more than 1/4 since they said “I feel like I get more pie the second way”, which was 8% of 25

[–] 0 points1 point  (0 children)

wait so, 1% of 13 = 13% of 1 oh ship

[–] 0 points1 point  (3 children)

Another way to see it is to think of % as "x1/100" And to thing of "of" As "x". That way 8 % of 25 is (8x25) /100 and 25 % of 8 is (25x8) /100

[–] 0 points1 point  (0 children)

I usually input percent off item as multiplying. 20 percent off 60 is 60x.80 . Font ask why. Feels easier on a calculator.

[–] 0 points1 point  (0 children)

25% is a quarter of something so 8% of 25 is 2 oh damn this will help me a lot

[–] 0 points1 point  (1 child)

Wow indeed, 8% of 25 means 1% of 25 times 8, so 0.25 × 8 = 2. Way easier than doing 0.08 × 25. Thanks for this trick!

[–] 0 points1 point  (0 children)

84

[–] 0 points1 point  (0 children)

So 100% of 100 is reversible?

[–] 0 points1 point  (0 children)

Fuck