Fucking math...
Submitted 3 weeks ago by Stamets@lemmy.dbzer0.com to science_memes@mander.xyz
https://lemmy.dbzer0.com/pictrs/image/38429cf3-bf24-4995-85b0-e2c61ca9baa8.webp
Comments
TheImpressiveX@lemmy.today 2 weeks ago
Carvex@lemmy.world 2 weeks ago
One…
A-two
A-three. Three licks to the Tootsie Roll center of a Tootsie Pop.
Lemminary@lemmy.world 2 weeks ago
Cat_Daddy@hexbear.net 2 weeks ago
Mr. Owl would be proud
ZoDoneRightNow@kbin.earth 2 weeks ago
0.04 x 75 == 0.75 x 4 == 75 x 4 x 0.01
berber@feddit.org 2 weeks ago
switch the order of the last two terms (the second equality), put the 0.01 in the middle, and it makes a bit more sense when read as calculation steps.
0.04 * 75 = 4 * 0.01 * 75 = 4 * 0.75ZoDoneRightNow@kbin.earth 2 weeks ago
That's fair. I intended them to just be a list of equalities
vane@lemmy.world 2 weeks ago
4*75/1003.5% of 7535*75/1000halvar@lemy.lol 2 weeks ago
Formulated like this it’s really obvious why the method up there works too
Noite_Etion@lemmy.world 2 weeks ago
This is the way
BigBenis@lemmy.world 2 weeks ago
That’s a neat trick but also 4% of 75 = (1% of 75) * 4 = 0.75 * 4 = 1.5 * 2 = 3
someacnt@sh.itjust.works 2 weeks ago
Ah, joy of commutative algebra.
Wait until you get to noncommutative algebra… shudders. No one who mastered that monster of a subject is sane in any measure.
Sunrosa@lemmy.world 2 weeks ago
Yay for quaternions and beyond
kamen@lemmy.world 2 weeks ago
I encountered those in game dev a while ago. Honestly, fuck them.
zout@fedia.io 2 weeks ago
I'd do 4%=1/25, 75/25=3.
gravitas_deficiency@sh.itjust.works 2 weeks ago
Is it weird that I just went
start: 75
to actual decimal: .75 22: 1.5 -> 3
LifeInMultipleChoice@lemmy.dbzer0.com 2 weeks ago
Nah we all do weird shit. I did 4x75, then moved from 300. to 3
Zulu@lemmy.world 2 weeks ago
Meanwhile im the idiot thats like “uh 10% of 75 is 7.5, half it for 5% of 75 is 3.75, 1% of 75 is .75, so its probably 3?”
Lets pray thats one of the options on the multiple choice. Oh the professor wants me to show my math? Well lets hope he’s open to me being an abstract dumbass that is capable of getting the right answer.
Lemminary@lemmy.world 2 weeks ago
Yes, but then I have to do 4 x 75 = 50 + 25 + 50 + 25 + 50 + 25 + 50 + 25 = 50 + 50 + 50 + 50 + 25 + 25 + 25 + 25 = 200 + 100 = 300 in that same order because non-maths brain.
idiomaddict@lemmy.world 2 weeks ago
I just figured 4% is 1/25 and divided 75/25
muhyb@programming.dev 2 weeks ago
That’s how my brain works as well.
Soot@hexbear.net 2 weeks ago
(4/100) * 75 = (75/100) * 4
I actually think the mutability of expressions is an under-taught part of maths until you reach like, constructing high-level proofs. Rearranging numbers into already-understood ones is a very useful skill.
ivanafterall@lemmy.world 2 weeks ago
I only learned this a few months ago here on Lemmy and still don’t believe it. It’s magic. You think you’re going to get it this time, but nope! Still works somehow!
jumjummy@lemmy.world 2 weeks ago
What’s funny is that if someone said (a*b)c is the same as (cb)*a, you’d probably say “of course it is”.
Same trick here if you show it as (4* 1/100) * 75 rewritten as (75 * 1/100) * 4.
Korhaka@sopuli.xyz 2 weeks ago
Even the first one, 0.75 doubled and then doubled again is hard?
affiliate@lemmy.world 2 weeks ago
at this point in my life, as somebody with multiple math degrees, if i ever come across a situation where i need to multiply or divide numbers and one of them is bigger than 12, im going to use a calculator.
darvocet@infosec.pub 2 weeks ago
Look at Mr big brain over here who learned his times tables. Sure hope nobody takes his lunch money.
Objection@lemmy.ml 2 weeks ago
Shitty Math Pro Tip: If you ever have to work with numbers larger than 10, convert it to scientific notation and then round to a single significant figure.
? = 0.04 x 75 ? = (4 x 10^-2) x (7.5 x 10^1) ? ~= (4 x 10^-2) x (8 x 10^1) ? = 4 x 8 x 10^-1 ? = 32 x 10^-1 ? = 3.2 ? ~= 3
See how easy that is? Here’s another one:
? = 12 x 12 ? = (1.2 x 10^1) x (1.2 x 10^1) ? ~= (1 x 10^1) x (1 x 10^1) ? = 1 x 10^2 ? = 100
Bam, lock it in.
KeenFlame@feddit.nu 2 weeks ago
Ya
Corkyskog@sh.itjust.works 2 weeks ago
0.75*4
Entropy_Pyre@lemmy.ca 2 weeks ago
Why did no one ever teach me this?? Did I miss this day in class? I feel so silly. This is really useful.
TwilightKiddy@programming.dev 2 weeks ago
Most teachers will write it off as obvious. Taking a percentage of something is just multiplication and if you actually write it down with multiplication, it is, indeed, obvious:
4*75/100=75*4/100And yes, it means you can just multiply 75 by 4 first and then divide by 100.
BanMe@lemmy.world 2 weeks ago
Yes and no, other day I was trying to figure out 17% of a number like 65, and I’m like “Oh it’s just 65% of 17!” Which really wasn’t helpful.
It works with small numbers on one side tho.
callyral@pawb.social 2 weeks ago
75% = 3/4
(3/4) * 4 = 3
Eheran@lemmy.world 2 weeks ago
Sure with easy numbers multiplication is easy. Try anything else.
BigPotato@lemmy.world 2 weeks ago
Yeah, this will be so helpful when I’m trying to figure out 20% of 36.23!
Look, move the decimal one to the left, you’ve now got 10%. Double that and you’ve got 20%. How often are y’all trying to find out percentages of nice even numbers like that?
Trainguyrom@reddthat.com 2 weeks ago
See I love quick and dirty rules to get close enough through estimation for whatever I’m mental mathing, because if I need exact numbers I’m turning to a computation device
20% of 36.23 I’d be going “okay 20% of 10 is 2, 3 10s in 36 so 3x2=6, and 6.23 is pretty close to half 10 and half 2 (from my previous 20% of 10 calculation) is 1 so 20% of 36.23 is slightly more than 7”
36.23% of 20 I’d be going “30% of 10 is 3, 2 10s in 20 so 2x3=6, 6.23% is close to 5 so half of 3 is 1.5, 6+1.5=7.5 so 36.23% of 20 is a bit more than 7.5”
Now which is closer to correct? Ehh I’m not sure I haven’t used a calculator yet, but I’m mental mathing so chances are my estimation got me close enough that I can just round to whichever direction is safer for errors and call it good. Usually I’m mental mathing to figure out splitting a bill, a tip or to double check some machine computed math that looks wrong, and none of those call for perfect precision, just getting close enough that it doesn’t matter
alsimoneau@lemmy.ca 2 weeks ago
×2÷10 7.246
Zerush@lemmy.ml 2 weeks ago
I also remember a somewhat sinister question: Using a knife, divide 3 apples among 4 people. 💀
betanumerus@lemmy.ca 2 weeks ago
4 over 100
X over 75
And there’s your butterfly.
LegoBrickOnFire@lemmy.world 2 weeks ago
4% is 1/25. 75 is 3*25. so the answer is 3!
Natanael@infosec.pub 2 weeks ago
3! = 3*2*1 = 6
LegoBrickOnFire@lemmy.world 2 weeks ago
That’s the same order of magnitude, so still correct!
Agent641@lemmy.world 2 weeks ago
Just do (7-5)+(5-4)=3
ngdev@lemmy.zip 2 weeks ago
i prefer the easier to remember (7 * 4) - (5^(√4))
ChaoticNeutralCzech@feddit.org 2 weeks ago
Asian Superman knows this
stevedice@sh.itjust.works 2 weeks ago
No. Stop it. Just multiply them together. This is useless.
titanicx@lemmy.zip 2 weeks ago
This only works in small cases.
idegenszavak@sh.itjust.works 2 weeks ago
My engineering brain says it’s 3.25.
4% is ~ 5%. 10% of 75 if 7.5. To get the 5% I have to divide it by 2, so 4% of 75 is close to 3.25. I will have to multiply it with some safety coefficient at the end, so the exact value doesn’t matter.
SatansMaggotyCumFart@piefed.world 2 weeks ago
That’s why you can always double the maximum limits engineers give.
60 mph roadway?
I can do 120 on it no problem.
Eight person elevator? Sixteen.
0.08 BAC? 0.16 easy peasy.
idegenszavak@sh.itjust.works 2 weeks ago
Yes, in elevators usually one cable could hold far more than the full weight, than they add 6 more for the safety.
For rail speed limits this is the exact way they calculate it. For road speed limits they consider break distance, which grows by the square of your speed, so if you go 120 on 60 road, you will need 4 times the distance to stop. I wrote 1.5 as a safety factor, not 4, With a 1.5 safety factor you can go by 75 though, but I would use a 1.1 safety there, as in my country the speed cameras are set up that way, you can go +10% of the official speed limit, they only send a cheque if you went even quicker than that.
DancingBear@midwest.social 2 weeks ago
Can I also smoke two joints before I smoke two joints, and then smoke two more?
jballs@sh.itjust.works 2 weeks ago
Did engineers come up with that last one though?
saltesc@lemmy.world 2 weeks ago
Mine brain just does 0.75 × 4.
Thought process was…
One_Honest_Dude@lemmy.world 2 weeks ago
I’m confused by this statement, the answer is 3. Why do all these extra steps for a wrong answer?
idegenszavak@sh.itjust.works 2 weeks ago
It’s not wrong, it’s close enough. And the point it works with more numbers and more type of calculation. Let’s calculate 4% of 1243. That’s the same as 1243% of 4, right, much easier to calculate by simply changing the 2 numbers… While my method is the same, by simply rounding everything.
And in engineering you always multiply/divide your results by a 1.5 or 1.25 safety factor, depending on situation. So you don’t have to calculate exact results, just close enough. E.g. G is always 10m/s2. π is only 3.14, the other digits doesn’t matter.
zakobjoa@lemmy.world 2 weeks ago
That’s exactly why we have safety coefficients.
IhaveCrabs111@lemmy.world 2 weeks ago
Safety coefficients are for nerds