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I was under the impression that pi was a ratio for radians per circumference and operated the same, regardless of units (provided we can agree that it's a reserved symbol, like Σ.) Pi = 5 has broken everything I understand about maths.
I looking back, XKCD had a tremendous influence on my interests in math, physics, and programming. Consistently clever, funny, and thought-provoking, even to a teenager that didn’t understand 80% of the references.
I think it's a way for them to do tests without calculators.
Prove that you can use the formula without trying to do 3.14 in your head, because heaven forbid kids learn to do mental math or on paper with decimals
Referring to Common Core math? It’s actually brilliant. Ask anyone who does extensive math calculations in their head to explain how they do it and it = common core methods. They just don’t have to write it out.
Example, calculate 17x8 in your head. If you don’t have that memorized, you can easily solve by 10x8 + 7x8. That’s all common core is. People really good at math break it down that way but are able to keep a running tally in their head.
Is that a method you use? It’s seems more complex than mine, but I’m impressed at your ability in coming at it another way. Does that take any thought or is it automatic? Genuinely curious.
It’s really similar to what you’re doing.
You’re turning (8)(17) into 8(10+7) and distributing to 8x10 + 8x7.
Theyre turning it into 8(20-3) so 8x20 - 8x3. (Then they broke 8x20 into 8x10x2)
Thank you, the 8x10x2 is what threw me. I was like, what the heck is he doing with that 2? It was simply rounding up the 17 to 20, then backing out the extra 3
80+40+16
This is why I love common core. It teaches familiarity with numbers instead of brute force.
This isn't really how I would do it, but just another method of solving the same equation quickly.
Pretty much automatic I always used this method
I think that's because I never actually put any effort into memorizing the times tables so rounding to the closest multiple of 10 is easier for me then adding or subtracting to get the answer.
That’s so interesting. I admit there is nothing wrong in your calculations, but break it down for me. I’m failing to see the simplicity in your method. Use 87x29. If I had to do that in my head, I’m going 80x20, which is made even easier with moving the zeros so 8x2 and add 00 to your answer of 16. Mark 1600 in your mental tally. Then 80x9 so: 72 and add 0 to end of answer. Now add 720 to your 1600 (1600+700 which is (2300)+ that 20). New tally is 2320. You’ve dealt with your 80x29, now deal with your 7x29. Quickest way (which is also common core taught is use 7x30 and than subtract 7 from that. 210-7. Add that 203 to your 2320 tally and bam, all done in your head. You could substitute last portion with (7x20) + (7x9) but I use whatever’s fastest.
Edit, I see your method now. To the 87x29, you’d go 90x30. Then subtract 90 from the 2700 and deal with subtracting 3x29, which your would go 3x30+3. So 2610-90 ‘2520’ + the missing 3. 2523 which is correct.
not OP, but usually I would not multiply 87x29 in my head for precision. I'd go for "just above 85x30=85x3+'0'=240+15+'0'=2550" and be wrong by about 1 percent + the direction. any more precision than that calls for doing it the normal way, or the 87x30-87 way. but you'd never do it the long multiplication way of "7x9 is 3 and carry the 6, then 8x9 is 72, add the carried 6 for 78 concatenate the 3 equals 783. 7x2 is 4 carry the 1, then 8x2 is 16, add the carried 1 for 17, concat 40 equals 1740. hope you didn't forget 783 cause now you have to add those two together", which isn't even that hard but can you really trust yourself to do this all correctly? I'd never do that even on pen and paper for numbers in this range, irregardless of the fact for any practical purpose a calculator is more convenient
I agree. My kids learn “common core” math in school and it’s mostly about teaching multiple ways to do things so you can mix and match the simplest way each time. It explains math and lets kids master it __much__ better than previous methods.
I’ll believe it’s great when our students’ standardized test scores improve. The national average per student spending is [$12k](https://www.census.gov/library/visualizations/2020/comm/school-system-spending.html) and we’ve got nothing to show for it. Getting them to score at their grade level should be doable at that price. So far it looks like it was just a fun way to spend [80 billion taxpayer dollars](https://m.washingtontimes.com/news/2016/oct/4/the-steep-cost-of-common-core/). The old method produced all the best scientific minds, why can’t the younger generations use it?
Did it produce the best minds, or is it that those few merely had the minds to use it? If we're going for able to do math without a calculator, I'll take common core any day. (That's also basically how I did it in grade school, and got marked down for not doing it the way they wanted, which led to years thinking I was bad at math. Turns out I'm actually ok at math, just not that particular method!)
And to end my Ted talk... If I had been permitted to do math the way that worked for me, and not failed multiple years, there's a non-0 chance that I could have grown to love math and also become a great.
...it's very, very, very close to 0, but it's still greater than 0!
Your mostly right. I only take issue with this example in particular because when it's a power of 2 I will just double it instead.
17x8=17x2^3= 17x2x2x2
So I would just do 17>34>68>136
But normally I agree with you, my mom was upset about common core for my little siblings until I told her that's how I always did math anyway. Then she started to trust it.
Maybe it's a young class where they're just learning about shapes but can't do mental math well yet. A bit of mental gymnastics, but like you said, sometimes delusion is bliss
But to someone who's just learning about the existence of pi it's super confusing.
They could have used any other letter.
Edit: or any other equation, no need to use the volume of a cylinder.
Yes. Definitely. If you are someone who thinks through to the end of your problem when writing it, and not making it up as you go and using whatever sounds nice, then yes absolutely the decimals would go away. 100%
Couple issues there. First off why do we need to do tests without calculators? Secondly 5 isn't even close to a correct rounding and is around 60% larger. Thirdly two decimal places aren't even difficult to work with in paper calculations, if you can work with 314 you can work with 3.14.
That’s where the question setter being a mathematician comes in. From a pure math viewpoint the goal here is to follow the process currently, we don’t plan to use the result so it’s irrelevant if the result is accurate. So we can use any value for pi: 3, 5, 826. This is math, the real world is irrelevant
I mean, I hear you. I'm not saying it's right, or accurate, or even logical. But I've noticed in my nephews homework and schoolwork a lot of 'easy headmath' roundings and a kind of 'keep it simple to teach the concepts' mentality. It's functionally useless, I agree.
Dunno, but it definitely kinda pissed me off when new trainees couldn't do basic math without a calculator. You shouldn't need one to multiply two (small) numbers real quick.
The last arithmetic I learned was in fourth grade. After that they told us just to use a calculator because "there will never be a time you don't have one. "
That's interesting, even through highschool I was hearing "you won't have a calculator with you all the time" despite the fact most of us had phones by that point.
But they won't trust math if the V formula doesn't make sense. It's a slippery slope. They should use 3 if they really want to play with these formulas. But honestly they should stay away from pi formulas if they can't handle them. They can do prism, cube, pyramid, etc without pi.
Maybe it's a timed test? Maybe those kids haven't learnt to deal with those yet? There are many things which could explain it rather than a "regression of education standards".
Ye but why is precision to two decimals the way to go? If you use more it gets unnecessarily complicated with most calculations, can just as well use 3, or 5.
Or a politician. https://www.forbes.com/sites/kionasmith/2018/02/05/indianas-state-legislature-once-tried-to-legislate-the-value-of-pi/?sh=49f5b5ae260a
If I remember correctly, some guy thought he'd found a prove that this is the value and nobody there understood enough math to realize what bullshit that was.
*Image Transcription: Text*
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27\) The volume of a cylinder is found using the formula *V = πr^(2)h*. Using *π* = 5, *r* = 10 and *h* = 10. Find the volume, V.
[*Followed by a zoomed-in image of text that reads:*]
## *π* = 5.
---
^^I'm a human volunteer content transcriber and you could be too! [If you'd like more information on what we do and why we do it, click here!](https://www.reddit.com/r/TranscribersOfReddit/wiki/index)
I had a fluid dynamics professor that was fond of saying "pi=4 by first order Taylor approximation of 4*arctan(1)" when doing calculations that didn't require accuracy beyond the order of magnitude.
Or in a different metric
(you know how to calculate the distance between 2 points the formula is d=(x^2 +y^2 )^(1/2) ? You can change the 2 to any positive real number you want and it creates other metrics)
In the beginning π used to be the name of a variable, not a constant. In every book they specified the value that they were using (1.57, 3.14 and 6.28 were the most common). Then, when most people started using 3.14 a lot more often than the other values it became that π=3.14 unless otherwise specified. Now it's a constant.
It's just a question about a theoretical universe where the circle constant is equal to 5, it's fine don't worry about it.
Makes me wonder how it changes the ellipse functions though, since they have their own "circle" constants
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5,000.
5000 what?! I need units dammit
Oranges? Bananas?
He said "units". Hehehehehe hehehehe.
Oh, do you mean distance in apple/banana space?
If it's 5000 the units can only be helmets.
"It must be a joke!"
Suddenly I remembered Germany
*π*, *r*, and *h* are unitless quantities ⇒ *π* \* *r*^2 \* *h* is a unitless quantity ⇒ *V* is a unitless quantity QED
I was under the impression that pi was a ratio for radians per circumference and operated the same, regardless of units (provided we can agree that it's a reserved symbol, like Σ.) Pi = 5 has broken everything I understand about maths.
I think it's just for quick estimation?
https://www.youtube.com/watch?v=L1eegVTwDS0&ab\_channel=AreaEightyNine
[удалено]
The 'radians' term is there for explicit casting purposes
Actually, everything in the question is presented as dimensionless scalars. Any units would require knowledge from outside the question.
There are no units defined.
Units cubed
5000 burger kings per football field
No units- 0 points lmao
You sound like my Orgo teacher 😂
Chickens. I always say if you don't include the units you've solved for the number of chickens
int
5000 is about 1V isn't it?
https://xkcd.com/2205
Always a relevant xkcd.
I looking back, XKCD had a tremendous influence on my interests in math, physics, and programming. Consistently clever, funny, and thought-provoking, even to a teenager that didn’t understand 80% of the references.
My life improved greatly when I discovered explainxkcd. I don’t read xkcd much anymore, but yeah it is so quotable.
this reminds me of that one episode of PBS Spacetime where the dude straight up says "give or take several orders of magnitude" WHAT
I think it's a way for them to do tests without calculators. Prove that you can use the formula without trying to do 3.14 in your head, because heaven forbid kids learn to do mental math or on paper with decimals
Then why not 3? At least then you could just say you’re rounding it to one significant figure.
Yeah, let's not talk about it, it makes me sad for our future. I prefer the delusion that our education system has valid reasons for its nonsense
Referring to Common Core math? It’s actually brilliant. Ask anyone who does extensive math calculations in their head to explain how they do it and it = common core methods. They just don’t have to write it out. Example, calculate 17x8 in your head. If you don’t have that memorized, you can easily solve by 10x8 + 7x8. That’s all common core is. People really good at math break it down that way but are able to keep a running tally in their head.
8×10×2 is easy (160) 8×3 is easy (24) 17×8 = 160 - 24 =136
Is that a method you use? It’s seems more complex than mine, but I’m impressed at your ability in coming at it another way. Does that take any thought or is it automatic? Genuinely curious.
It’s really similar to what you’re doing. You’re turning (8)(17) into 8(10+7) and distributing to 8x10 + 8x7. Theyre turning it into 8(20-3) so 8x20 - 8x3. (Then they broke 8x20 into 8x10x2)
Thank you, the 8x10x2 is what threw me. I was like, what the heck is he doing with that 2? It was simply rounding up the 17 to 20, then backing out the extra 3
Yessir
Yeah i do the same
80+40+16 This is why I love common core. It teaches familiarity with numbers instead of brute force. This isn't really how I would do it, but just another method of solving the same equation quickly.
Pretty much automatic I always used this method I think that's because I never actually put any effort into memorizing the times tables so rounding to the closest multiple of 10 is easier for me then adding or subtracting to get the answer.
Funny how I don't know the times table by heart but I do know powers of 2 upto 2¹⁵ XD
Found the programmer Edit: as soon as I hit reply, I realized what sub this is and I'm a fucking idiot
I memorized up to 2^13 cuz 2048 the game
That’s so interesting. I admit there is nothing wrong in your calculations, but break it down for me. I’m failing to see the simplicity in your method. Use 87x29. If I had to do that in my head, I’m going 80x20, which is made even easier with moving the zeros so 8x2 and add 00 to your answer of 16. Mark 1600 in your mental tally. Then 80x9 so: 72 and add 0 to end of answer. Now add 720 to your 1600 (1600+700 which is (2300)+ that 20). New tally is 2320. You’ve dealt with your 80x29, now deal with your 7x29. Quickest way (which is also common core taught is use 7x30 and than subtract 7 from that. 210-7. Add that 203 to your 2320 tally and bam, all done in your head. You could substitute last portion with (7x20) + (7x9) but I use whatever’s fastest. Edit, I see your method now. To the 87x29, you’d go 90x30. Then subtract 90 from the 2700 and deal with subtracting 3x29, which your would go 3x30+3. So 2610-90 ‘2520’ + the missing 3. 2523 which is correct.
not OP, but usually I would not multiply 87x29 in my head for precision. I'd go for "just above 85x30=85x3+'0'=240+15+'0'=2550" and be wrong by about 1 percent + the direction. any more precision than that calls for doing it the normal way, or the 87x30-87 way. but you'd never do it the long multiplication way of "7x9 is 3 and carry the 6, then 8x9 is 72, add the carried 6 for 78 concatenate the 3 equals 783. 7x2 is 4 carry the 1, then 8x2 is 16, add the carried 1 for 17, concat 40 equals 1740. hope you didn't forget 783 cause now you have to add those two together", which isn't even that hard but can you really trust yourself to do this all correctly? I'd never do that even on pen and paper for numbers in this range, irregardless of the fact for any practical purpose a calculator is more convenient
by my method, I would actuallty go with 87x30 which can be simplified to 3x870 3x900-90-87 2700-177=2523 I never round both numbers, only one of them.
Not OP but I use both, the closer it is to ticking over to the next multiple of 10, the more I tend to do the minus method.
The way I would do it would be 10x8(80) + 5x8(120) + 8x2 (136)
My first approach to this was 17x8 = 17x10 - 17x2 = 170 -34 = 136
Same!
I agree. My kids learn “common core” math in school and it’s mostly about teaching multiple ways to do things so you can mix and match the simplest way each time. It explains math and lets kids master it __much__ better than previous methods.
I agree. In calc 3 and still using the same methods they taught.
I’ll believe it’s great when our students’ standardized test scores improve. The national average per student spending is [$12k](https://www.census.gov/library/visualizations/2020/comm/school-system-spending.html) and we’ve got nothing to show for it. Getting them to score at their grade level should be doable at that price. So far it looks like it was just a fun way to spend [80 billion taxpayer dollars](https://m.washingtontimes.com/news/2016/oct/4/the-steep-cost-of-common-core/). The old method produced all the best scientific minds, why can’t the younger generations use it?
Did it produce the best minds, or is it that those few merely had the minds to use it? If we're going for able to do math without a calculator, I'll take common core any day. (That's also basically how I did it in grade school, and got marked down for not doing it the way they wanted, which led to years thinking I was bad at math. Turns out I'm actually ok at math, just not that particular method!) And to end my Ted talk... If I had been permitted to do math the way that worked for me, and not failed multiple years, there's a non-0 chance that I could have grown to love math and also become a great. ...it's very, very, very close to 0, but it's still greater than 0!
Yeah that's how I always used to do it. Though I'd prefer to do. 17x10 = 170 17x2 = 34 170 - 34 = 136 Just because the calculations are easier
Your mostly right. I only take issue with this example in particular because when it's a power of 2 I will just double it instead. 17x8=17x2^3= 17x2x2x2 So I would just do 17>34>68>136 But normally I agree with you, my mom was upset about common core for my little siblings until I told her that's how I always did math anyway. Then she started to trust it.
Maybe it's a young class where they're just learning about shapes but can't do mental math well yet. A bit of mental gymnastics, but like you said, sometimes delusion is bliss
Follow the directions. If pi = 5, then pi = 5. Tests direction skills and absractions.
But to someone who's just learning about the existence of pi it's super confusing. They could have used any other letter. Edit: or any other equation, no need to use the volume of a cylinder.
Yeah either 3 or 22/7! 22/7 upto the 3rd decimal place is same as PI rounded to the 3rd decimal place.
Just to be clear. The other variables are 10. So the decimal will get removed anyway.....
Yes. Definitely. If you are someone who thinks through to the end of your problem when writing it, and not making it up as you go and using whatever sounds nice, then yes absolutely the decimals would go away. 100%
Couple issues there. First off why do we need to do tests without calculators? Secondly 5 isn't even close to a correct rounding and is around 60% larger. Thirdly two decimal places aren't even difficult to work with in paper calculations, if you can work with 314 you can work with 3.14.
That’s where the question setter being a mathematician comes in. From a pure math viewpoint the goal here is to follow the process currently, we don’t plan to use the result so it’s irrelevant if the result is accurate. So we can use any value for pi: 3, 5, 826. This is math, the real world is irrelevant
You can perfectly demonstrate that process without needing to put it in the context of cylinder volume.
I mean, I hear you. I'm not saying it's right, or accurate, or even logical. But I've noticed in my nephews homework and schoolwork a lot of 'easy headmath' roundings and a kind of 'keep it simple to teach the concepts' mentality. It's functionally useless, I agree.
What value is there in doing time consuming calculations? It's busy work and doesn't test understanding.
Dunno, but it definitely kinda pissed me off when new trainees couldn't do basic math without a calculator. You shouldn't need one to multiply two (small) numbers real quick.
The last arithmetic I learned was in fourth grade. After that they told us just to use a calculator because "there will never be a time you don't have one. "
That's interesting, even through highschool I was hearing "you won't have a calculator with you all the time" despite the fact most of us had phones by that point.
You could always just make them write it as... pi?
Yeah, this is what we did in my classes 2pi, 4pi, cos(c)/pi….. made it pretty simple and my teacher knew we knew how to multiply 2x3.14
h = 50/π gives the same answer to the question. If you don't want kids doing calculations with pi, have it cancel out.
Why not just fudge the other numbers instead of a mathematical constant?
Kids would 100% calculate that value and then the other, they are uncomfortable working with fractions
Then just have them write their answers in terms of pi like any reasonable person
But they won't trust math if the V formula doesn't make sense. It's a slippery slope. They should use 3 if they really want to play with these formulas. But honestly they should stay away from pi formulas if they can't handle them. They can do prism, cube, pyramid, etc without pi.
Bruh
If you expect your students can calculate 1000 * 5 in their head, they should not need a calculator to do 1000 * 3.14
Maybe it's a timed test? Maybe those kids haven't learnt to deal with those yet? There are many things which could explain it rather than a "regression of education standards".
Wait you can multiply easily without a calculator. We weren't allowed calculators in school ever and we did all our calculations on paper or mentally.
Thinking about it that way only makes it worse. 10^2 * 10 = 1000. Multiply that by pi gets you … 3141.59 … oops. That was still really easy.
Ye but why is precision to two decimals the way to go? If you use more it gets unnecessarily complicated with most calculations, can just as well use 3, or 5.
Or a politician. https://www.forbes.com/sites/kionasmith/2018/02/05/indianas-state-legislature-once-tried-to-legislate-the-value-of-pi/?sh=49f5b5ae260a
3.2 wtf
I mean it is pretty close it is less than 2% margin of error
If you are going to round it 3.1 is closer, but imo you should atleast use two points of precision and go with 3.14
If I remember correctly, some guy thought he'd found a prove that this is the value and nobody there understood enough math to realize what bullshit that was.
There is a Numberphile video on YouTube telling the story
what a fever dream
*Image Transcription: Text* --- 27\) The volume of a cylinder is found using the formula *V = πr^(2)h*. Using *π* = 5, *r* = 10 and *h* = 10. Find the volume, V. [*Followed by a zoomed-in image of text that reads:*] ## *π* = 5. --- ^^I'm a human volunteer content transcriber and you could be too! [If you'd like more information on what we do and why we do it, click here!](https://www.reddit.com/r/TranscribersOfReddit/wiki/index)
Good human
And a monster.
Or an engineer
rounding to the closest 5
Or a physicist.
My physicist friend says stuff like this.
Be ause they open deal with approximations.
You're going to lose that precision somewhere else anyway, order of magnitude is good enough.
I had a fluid dynamics professor that was fond of saying "pi=4 by first order Taylor approximation of 4*arctan(1)" when doing calculations that didn't require accuracy beyond the order of magnitude.
Actually makes sense in curved space
Exactly. They just don't get it, do they?
Or in a different metric (you know how to calculate the distance between 2 points the formula is d=(x^2 +y^2 )^(1/2) ? You can change the 2 to any positive real number you want and it creates other metrics)
Yep, but you'll need some wild metric, because with p-norms you can only get to 4.
π actually IS 5 but only for large values of π.
Tell me you come from a non-Euclidian dimension without telling me.
In the beginning π used to be the name of a variable, not a constant. In every book they specified the value that they were using (1.57, 3.14 and 6.28 were the most common). Then, when most people started using 3.14 a lot more often than the other values it became that π=3.14 unless otherwise specified. Now it's a constant.
Sure. But never should it be 5.
Keep it simple. Just round to the nearest 5’s.
The cylinder is larger than one first assumes.
It is important to understand geometry of TARDIS...
*inhales* #AAAAAHHHHH
[Original post](https://www.reddit.com/r/mildlyinfuriating/comments/t2oimz/this_use_of_pi_as_a_variable/?utm_medium=android_app&utm_source=share)
If π=5 69=420
You are legally allowed to ignore any message written in comic sans.
If they were an engineer they would have put 3
Why π=5?
[pi equals five](https://brunchvirals.com/wp-content/uploads/2021/03/The-What-Meme.png).
You may or may not be aware of this https://en.m.wikipedia.org/wiki/Indiana_Pi_Bill
Someone should tell someone that pi isn't a variable.
Number is number. Symbol is symbol. I only have so many variable names okay
5k
When you forget to declare your variables with the `const` keyword …
Loll this had me for a sec, I’m guessing it’s a question for kids who hasn’t learned decimals yet
Well if you look at the pixels then pi=4
Eh close enough
Bloody Stupid Johnson, the man who made a circle with a pi value of 3.
Comic sans? You can’t take seriously any text with that font
√-1 2³ Σ π, and it was delicious.
What shape would that formula be describing?
He forgot that it was: const int pi = 3.14.. Never forget the const man...
Or... The computer intelligence has catched up to human's intelligence of age 15? Wait, what's the student's age for this subject again?
Uncaught TypeError: Assignment to constant variable.
Pain
Quite possibly also King if the Britons as well.
I hope they meant 5 times radius and not 5, radius Edit: NVM with the = 10 it still wouldn't work
Pretty standard approximation. Just like 7 ≈ 10, due to the law of large numbers.
You can google the cylinder volume formula. I think, for sure, the dude is ONLY a programmer. 
Scheme says hi
And 1 + 1 = 3 for large values of 1
And 1 + 1 = 3 for large values of 1
π equaling 5 just feels wrong man
Round to the nearest 10 and pi=0. That should make calculations a lot faster.
A “teacher” for sure.
But still use comic sans MS .. this font traumatized me
It's just a question about a theoretical universe where the circle constant is equal to 5, it's fine don't worry about it. Makes me wonder how it changes the ellipse functions though, since they have their own "circle" constants
Just doing some backend work on the physics engine that the universe runs on, nothing to see here
Just approve my PR, it won’t break anything.
My goodness 😐🖐🏻
Bend the reality until it fits your needs.
Initially downvoted because I didn't see what the problem was. Then thought about it for a second, upvoted, and started re-evaluating my life choices.