I wrote a (very long) blog post about those viral math problems and am looking for feedback, especially from people who are not convinced that the problem is ambiguous.
It's about a 30min read so thank you in advance if you really take the time to read it, but I think it's worth it if you joined such discussions in the past, but I'm probably biased because I wrote it :)
Division comes before Multiplication, doesn't it? I know BODMAS.
That makes no sense. Division is just multiplication by an inverse. There's no reason for one to come before another.
This actually explains alot. Murica is Pemdas but Canadian used Bodmas so multiply is first in America.
As far as I understand it, they're given equal weight in the order of operations, it's just whichever you hit first left to right.
Ah, but if you use the rules BODMSA (or PEDMSA) then you can follow the letter order strictly, ignoring the equal precedence left-to-right rule, and you still get the correct answer. Therefore clearly we should start teaching BODMSA in primary schools. Or perhaps BFEDMSA. (Brackets, named Functions, Exponentiation, Division, Multiplication, Subtraction, Addition). I'm sure that would remove all confusion and stop all arguments. ... Or perhaps we need another letter to clarify whether implicit multiplication with a coefficient and no symbol is different to explicit multiplication... BFEIDMSA or BFEDIMSA. Shall we vote on it?
Don't need any extra letters - just need people to remember the rules around expanding brackets in the first place.
Obviously more letters would make the mnemonic worse, not better. I was making a joke.
As for the brackets 'the rules around expanding brackets' are only meaningful in the assumed context of our order of operations. For example, if we instead all agreed that addition should be before multiplication, then a×(b+c) would "expand" to a×b+c, because the addition is before multiplication anyway and the brackets do nothing.
Fair enough, but my point still stands.
...then you would STILL have to do multiplication first. You can't change Maths by simply agreeing to change it - that's like saying if we all agree that the Earth is flat then the Earth is flat. Similarly we can't agree that 1+1=3 now. Maths is used to model the real world - you can't "agree" to change physics. You can't add 1 thing to 1 other thing and have 3 things now, no matter how much you might want to "agree" that there is 3, there's only 2 things. Multiplying is a binary operation, and addition is unary, and you have to do binary operators before unary operators - that is a fact that no amount of "agreeing" can change. 2x3 is actually a contracted form of 2+2+2, which is why it has to be done before addition - you're in fact exposing the hidden additions before you do the additions.
The brackets, by definition, say what to do first. Regardless of any other order of operations rules, you always do brackets first - that is in fact their sole job. They indicate any exceptions to the rules that would apply otherwise. They perform no other function. If you're going to no longer do brackets first then you would simply not use them at all anymore. And in fact we don't - when there are redundant brackets, like in (2)(1+2), we simply leave them out, leaving 2(1+2).
I believe you're conflating the rules of maths with the notation we use to represent mathematical concepts. We can choose whatever notation we like to mean anything we like. There is absolutely nothing stopping us from choosing to interpret a+b×c as (a+b)×c rather than a+(b×c). We don't even have to write it like that at all. We could write a,b,c×+. (And sometimes people do write it like that.) Notation is just a way to communicate. It represents the maths, but it is not itself the maths. Some notation is more convenient or more intuitive than others. × before + is a very convenient choice, because it easier to express mathematical truths clearly and concisely - but nevertheless, it is still just a choice.
You think a Maths teacher doesn't know the difference?
Yes there is - the underlying Maths. 2x3 is short for 2+2+2, which is therefore why you have to expand multiplications before doing additions. If you "chose" to interpret 2+3x4 (which we KNOW is equal to 14, because 3x4=3+3+3+3 by definition) as (2+3)x4, you would get 20, which is clearly wrong, since 20 isn't equal to 14.
No that's right, because it IS written differently in different languages, but regardless of how you write it, it doesn't change that 2+3x4=14 - the underlying Maths doesn't change regardless of how you decide to write it. Maths is literally universal.
It's not a choice, it's a consequence of the fact that x is shorthand for +. i.e. 2x3=2+2+2.
It is a consequence of the definitions of what each operator does. If x is a contraction of +, then we have to expand x before we do +. If it were the other way around then we'd have to do it the other way around. Anything which is a contraction of something else has to be expanded first.
Hey man, if you want to resort to some weird appeal to authority argument despite having clear examples against what you are saying - go for it. You can choose to die on that hill if you want to.
Which are where, exactly? You haven't presented any. You haven't, for example, shown how one can make (2+3)x4=14.
re: appeal to authority
The examples I gave were that the expansion of brackets would be done differently if the order of operations was "PESADM"; and I also drew your attention to the fact that reverse polish notation exists, in which there are no brackets at all and the order of operation is entirely determined by the order that operators appear, with no hierarchy of operations. As for your appeal to authority, let me just say that your level of qualification on this topic is not above mine. It adds no weight whatsoever to your argument.
I just glanced at your post history to get a sense of why you were so engaged in this. I was a bit startled to see that you've been on a bit of a posting spree in this thread, which I point out to you is a 3 month old post on a 'memes' channel. I see you've taken issue with a lot of what people have said here. My suggestion to you now is that there probably won't be a lot of engagement in this thread from this point on. So perhaps you should just ponder what is said, and prepare yourself again for next time this comes up. Perhaps you can start by seeing if you can get a consensus amongst fellow experts in a maths channel or something, because at the moment it seems like you're on your own.
Yep I read it, and no it wouldn't. Expanding Brackets - or in the case of this mnemonic Parentheses - is done as part of B/D (as the case may be). i.e. expanding brackets isn't "multiplication" (no multiplication sign), but solving brackets (there are brackets there), which always come first in all the mnemonics.
...but is not taught in high school.
Maybe not, but it means it's not an "appeal to authority" (as per screenshot). Maths teachers ARE an authority on Maths. The most common appeal to authority I see from people is claiming that someone (not them) is a University professor, and "they would know". No, they wouldn't - this topic isn't taught at university - it's taught in high school.
I'm a teacher. You say you're on the same level as me - don't you like to teach people what's correct?
Which will show up in search results for all eternity (it's how I found it - I was looking for something else!).
Got another 12 responses after yours. But the point is I'm not even LOOKING for responses, just to correct misinformation. As a teacher (a Maths teacher?) have you not had people say to you "But Google says"? I certainly have. It's the bane of my professions.
Did you read my thread? Maths textbooks, calculators, proofs, etc. Also, someone else said what you just did, asked a Maths teacher, and was told I was correct, then was man enough to go back and edit his posts and admit I was correct and specifically said "SmartmanApps is not on his own with this".
Yeah 100% was not taught that. Follow the pemdas or fail the test. Division is after Multiply in pemdas.
I put the equation into excel and get 9 which only makes sense in bodmas.
It doesn't make sense in BODMAS either. Expanding Brackets has precedence of... Brackets, not "multiplication" - "Multiplication" refers literally to multiplication signs, of which there are none in this question.
The y(n+1) is same as yn + y if you removed the "6÷" part. It's implied multiplication.
No, it's the same as (yn+y). You can't remove brackets unless there is only 1 term left inside.
...The Distributive Law.
Well I'm not seeing the difference here. Yn+y= yn+y = y(n+1) = y × (n +1) I think we agree with that.
Ok, that's a start. In your simple example they are all equal, but they aren't all the same.
yn+y - 2 terms
y(n+1) - 1 term
y×(n +1) - 2 terms
To see the difference, now precede it with a division, like in the original question...
1÷yn+y=(1/yn)+y
1÷y(n+1)=1/(yn+y)
1÷y×(n +1)=(n +1)/y
Note that in the last one, compared to the second one, the (n+1) is now in the numerator instead of in the denominator. Welcome to why having the (2+2) in the numerator gives the wrong answer.
Good example wish we had better math format.
The granger issue is I thought multiple always happens first. But apparently it's what's left side first.
Multiplication and division are equal precedence (and done left to right) if that's what you're talking about, but the issue is that a(b+c) isn't "multiplication" at all, it's a bracketed term with a coefficient which is therefore subject to The Distributive Law, and is solved as part of solving Brackets, which is always first. Multiplication refers literally to multiplication signs, of which there are none in the original question. A Term is a product, which is the result of a multiplication, not something which is to be multiplied.
If a=2 and b=3, then...
axb=2x3 - 2 terms
ab=6 - 1 term
That is what I am talking about. I would have got 1 by doing 2(2+2) = 8 first. Not because of bracket but because of "implied multiplication."
What I am learning here: 8÷2(2+2) is not same as 8÷2×(2+2)
For several reasons:
Yeah, right answer but wrong reason. There's no such thing as implicit multiplication.
Correct, and that's because of Terms - 8÷2(2+2) is 2 terms, with the (2+2) in the denominator, but 8÷2×(2+2) is 3 terms, with the (2+2) in the numerator... hence why people get the wrong answer when they add an extra multiply in.
Right, because it's not "multiplication" at all (only applies literally to multiplication signs), it's a coefficient of a bracketed term, which means we have to apply The Distributive Law as part of solving Brackets.
Yeah, the actual rule is Left associativity, and going left to right is the easy way to obey that.
Lol only tool 30 years to get thos far on basics.
Just proves, never too late to learn :-)
Thanks for the effort!
You're welcome.