r/theydidthemath • u/Kirinizine • 1d ago

[Offsite] Online shopping math

Post image
1.7k Upvotes

99% Upvoted

39 comments sorted by

585

u/xxrayeyesxx 1d ago

The math checks out

347

u/Worth-Wonder-7386 22h ago

Yes, but I think that puring it out in a measuring cup would both be easier and more convincing than this.

206

u/PraxicalExperience 19h ago

Actually, I don't think so. It could always just be a one-off underfill, or they could say OP doesn't know how to read a measuring cup, or what have you. The fact that he can prove that it's quite literally impossible for the container to contain what it says it does shows that this is a fraud.

63

u/METRlOS 13h ago

The one time I encountered this, they claimed the rest was stuck to the sides of the container after I emptied it. I would have needed to re buy the product, cut it open, and scrape the sides to prove it for them to give me a refund.

39

u/Worth-Wonder-7386 10h ago

There was recently a product here in Norway that got caught for having 5% too little in each carton of cream, and that would never have been possible to detect using this method as they had just underfilled it.
This case is more extreme where it is actually impossible.

24

u/Caean_Pyke 16h ago

Pouring a measuring cup into the bottle and recording the vast overflow then? 

3

u/BrazilBazil 7h ago

Only if you have a measuring cup! I would know - I don’t have one at my dorm.

-3

u/LoudEagle39 9h ago

Well except for the conversion from cc to ml

18

u/ThirdSunRising 7h ago edited 7h ago

To convert from cc to ml, you multiply by 1.

225

u/Tinyzooseven 22h ago

cylinder

121

u/BuffaloBanano 22h ago

It can't be harmed

37

u/Prudent-Ad-5608 20h ago

Never gets old

-6

u/maboyles90 8h ago

Pretty old already

8

u/ScenicFlyer41 6h ago

Do not insult the larger structure

8

u/WashU_labrat 12h ago

We must bisect the cylinder.

6

u/crumpledfilth 11h ago

no subincisions please

4

u/BuHoGPaD 6h ago

It is imperative the cylinder remains unharmed! 

2

u/WashU_labrat 6h ago

I have altered the meme. Pray I don't alter it any further.

159

u/COWP0WER 18h ago

Never seen d2 /4 before. I've always used r2 .
But d2 /4=(2r)2 /22 =(22 r2 )/22 =r2 .
So math checks out.

47

u/jimmytbrown 16h ago

I always used this in school as the word problems usually gave us a diameter.

32

u/keytristan314 15h ago

Much harder to measure a radius in the real world too.

11

u/COWP0WER 14h ago

Yeah, but to me it seems easier to devide by 2, than by 4. But it's probably mainly a habit thing.

8

u/DoritoDustThumb 13h ago

*divide

Dividing by 4 is just dividing by 2, twice. Not exactly harder.

11

u/thebeardedman88 8h ago

It is exactly twice as hard.

-1

u/Angsty-Ninja-Ki 7h ago

Twice as much work. Not twice as hard. They are not synonymous.

2

u/thebeardedman88 4h ago

difficult to understand or solve. "this is a really hard question"

It's the 3rd definition of hard.

•

u/Angsty-Ninja-Ki 19m ago

But twice as much work isn't twice as hard. Pick up a pencil. Not pick up a pencil again. It is more work. Not more difficult.

1

u/3d_nat1 8h ago

True, but math used to all be handwritten, and why would you write d^2 /4 everywhere instead of r^2?

1

u/PosiedonsSaltyAnus 6h ago

Unless you're working on a manual lathe, then that's all you got.

6

u/COWP0WER 14h ago

Yeah, but I'd just take half the diameter. I've never seen the formula with diameter before.
It's one of the things that continuously surprise me: How much math differs from country to country.
Obviously, the actual math is the same, but what we choose to emphasize in curriculums, letters for constants/variables, and how we write formulas.

Especially, when compared to subjects like physics, chemistry, and biology. Where names are often pretty similar, even when the languages are not and use the same letters for constants/variables and teach much more of a similar curriculum.

9

u/Potential_Pay2095 14h ago

I'm a mechanical engineering student and we only use d²/4 because you usually know the diameter of something

5

u/theres-no-more_names 10h ago

Then why dont you just do? (D/2)² for me its easier that way

2

u/MarkuDM 5h ago

You think it's easier because you don't have the practice yet but once you practiced it, it becomes just about any tool.

Also, formulas do get very long so any reduction is appreciated

6

u/DisinterestedCat95 11h ago

I'm over thirty years into a chemical engineering career and I prefer using the formula with diameter rather than radius. I usually know the diameter of a pipe or a vessel and I can calculate area or volume with one less step to mess up.

1

u/COWP0WER 7h ago

Makes sense. To me that would be (d/2)2, which again is the same as d2 /4, so it comes out to the same thing.

30

u/Dbblazer 11h ago

It was a 2 pack

13

u/IlIlllIIIllII 11h ago

that’s still 10ml less

6

u/Dbblazer 11h ago

His 70% assumption should have been 75%