this post was submitted on 31 Dec 2023
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It was just a number I picked for the proof - any number works!
We could! Let's go...
Teacher is writing a test. Decides the next question to be written will have 77 as the answer. How else can we write that? Let's start with 7+70. We know the answer to that is 77 because...
Now, we can also write that as a repeated addition. i.e. 7+10+10+10+10+10+10+10 - yet another way that we can write 77 (which we already know is the answer). What else?
We also know, by the definition of multiplication, that multiplication is short for repeated addition, so now let's rewrite that as 7+10x7, and we still know that the answer to this is 77 - all we have done is rewrite it in different ways based on the definitions of operators.
So now we need to look at what order of operations rules we need to make sure anyone doing this gets 77, because we already know the answer is 77!
So let's try addition first..
7+10x7=17x7=119. Nope, not 77, that doesn't work.
Now let's try doing multiplication first...
7+10x7=7+70=77. Yes! We got the right answer. Welcome to our first order of operations rule - multiplication before addition.
Let's see..
First let's pull out the 2...
14=2+12
Now let's pull out that 5...
14=2+7+5.
Can we make that 7 in the middle equal to the 3x4 you wrote? No, we can't. 3x4 by definition is equal to 3+3+3+3, which is equal to 12, which isn't equal to 7, so no, we can't write 14=2+3x4+5 by the definition of the operators of add and multiply.
Again, no order of operations in there, simply can we write this with our current Maths operator definitions, and the answer is no, we can't. i.e. the order of operations rules are derived from the definitions of the operators themselves. We can't write 14=2+3x4+5 while 3x4 is still defined to mean 3+3+3+3. To make your equation work, we would have to make 3x4=7, which is what + already means, and why would you make the multiply operator mean the same thing as the addition operator? That would be redundant.
I'm going from proof to proof.
By knowing how arithmetic works. The rules of Maths work for all numbers and all operators - they were written for that specific purpose!
Are you a visual learner? Do you want me to actually draw it up on a number line? Cos that's what it all boils down to - jumps on the number line. We're only dealing with 1 Dimensional Maths here.
Ok, I think I got something with 77.
So we start with 77. One way to make 77 is (7 * 10) + 7. But there are several ways to get 77. You can also do ((3 + 4) * 10) + 7 = 77. There are several different permutations up to and including 77 * 1. Ok, but none of that has anything to do with order of operations. Using parentheses we can ignore order of operations altogether.
Another way to look at it is to ask the question does 3 + 4 * 10 + 7 equal 77? Assuming the normal order of operations, it does not. But there is some order of operations that will get us 77 as seen above. Do you believe the statement above is true?
Assuming we use a completely reversed order of operations, we can get 77 this way. (7 * 10) + 7. This implies that the order of operations alone does not give you the correct answer. The combination between the equation and the order of operations that gives you the correct answer in infix notation. And because you can get the correct answer with any order of operations given that the equation is written correctly, then it follows that the order of operations is not critical for computation. To put it plainly the order of operations does not matter. We could use any order of operations and still do math correctly.
Yep, you nearly had it there. I've been saying this repeatedly in my proofs, but you've been missing what that means.
Only if you put them in the right place! With your example (7x10)+7=77, if we move the brackets 7x(10+7)=490, which is a different answer... which demonstrates why we can't change the order of operations - you get different answers. The order of operations rules are there to make sure everyone gets the same answer from the same expression.
Also, using brackets isn't ignoring the order of operations rules - brackets are part of the order of operations rules.
I already addressed a similar question like this from you in my previous post, and you've ignored my answer (sigh). I'll do this again and if you ignore my response again I'm giving up (it seems to me that you're just being disingenuous now, ignoring my responses to your examples which prove they don't work).
3+4x10+7
Recall that by definition - i.e. this is nothing to do with order of operations - 4x10=4+4+4+4+4+4+4+4+4+4
therefore...
3+4x10+7=3+4+4+4+4+4+4+4+4+4+4+7=50, which is not 77, so no, 3+4x10+7 does not equal 77, and again, that has nothing to do with order of operations, that is only using the definition of multiplication as repeated addition.
Huh?? That's not a reversed order of operations - that's our current order of operations! Multiply before adding!
WTH?! It PROVES that order of operations alone gives you the right answer. (7x10)+7=77. 7x10+7=77. Same answer, no brackets needed! Because of the order of operations rules.
No, you can't. 7+10x7 is written correctly, and we know the answer is 77. Let's try a different order of operations and do addition first. 7+10x7=70x7=490 which isn't 77, so it's wrong. There is only one order of operations which gives the correct answer of 77, and that's multiplication before addition and that's because multiplication is defined as being shorthand for addition!
I've shown you, repeatedly, that in fact it is. 490 is not equal to 77.
Only if getting the right answer "does not matter".
In what world exactly are 490 and 77 the same answer?
Okay. Well then it sounds like we agree.
It seems like we agree that we can't change the order of operations without changing the equations, otherwise we won't get the same answer.
I was never arguing against this.
All I was saying was that we could use any order of operations we want. It's just a way of interpreting the equation. We don't have to use the current order of operations. We could use a different order of operations. As long as we update the equations we use as well. So it doesn't really matter which order of operations we use.
For some reason I was getting pushed back from you on this. Now it seems like you have no problem with it.
So I think we agree also. I'm very confused how we got here in the first place.
Edit:
By the way, you can stop expanding x * 3 = x + x + x. I understand how multiplication works. I just don't find it a very convincing argument for why we have to use the current order of operations that we are using today. I think it has interesting historical note. I wouldn't be surprised if it was the basis for why we have the current order of operations. But I don't think it limits the order of operations we could use.
If you think that then you haven't understood anything I've said
No, we can’t change the order of operations without changing the definitions of the operators. We have to do multiplication before addition because multiplication is shorthand for addition. If you wanted to have a "different" order of operations, where we didn't do multiplication before addition, then multiplication can't be shorthand for addition anymore. To have a "different" order of operations, you could swap the definitions around, so that addition is shorthand for multiplication, and then yes, you would be doing addition before multiplication, but that's the only way you can change the order of operations - by changing the definitions of the operators to begin with... and you would still end up with what we have now, except you're calling addition "multiplication" and calling multiplication "addition". All you would've done in reality is swapped the names around.
No, we can't. And yes, you're only saying that - you haven't actually tried it. You gave me some examples which I proved don't work, and yet you're still saying the same thing whilst doing absolutely no Maths at all to back up that claim - it's just words, and I'm showing you that it doesn't work.
As with anything in Maths, there is a right way, and a wrong way. Only one way works. You might as well say "we could interpret 1+1 as equal to 3". Try doing some actual Maths using 1+1=3 and let me know how far you get.
The definitions.
It really does, otherwise you just get wrong answers. Again, you haven't actually tried doing it a different way, you just keep saying we could do it a different way (even though actually trying to do it a different way proves it doesn't work).
Because you're still saying the same thing you said to begin with - that we can "choose" to use a different order of operations. No we can't. The order of operations rules come directly from the definitions of the operators. If we define multiplication as being a shorthand form of addition, then that means we have to do multiplication before addition, it's that simple, yet you continue to not see it. Doing addition before multiplication only gives wrong answers.
No, you can't - they're the same thing! That's like saying "By the way, you can stop writing Maths as Mathematics". One is just an abbreviation of the other, and you're failing to see how multiplication being an abbreviation of addition means there's only one right answer and we can only get that answer by doing multiplication before addition, hence the order of operations rules!
Apparently not, or you'd understand why the order of operations rules are what they are.
2+3x4=2+3+3+3+3=14. That's it, that's the only correct answer by definition (I didn't use any order of operations rules there, just the definition of multiplication as shorthand for addition). Now, show me "a different order of operations" which still gives 14 as the answer. This is what your claim is, so prove it!
It's a proof. If you get the wrong answer with a different set of order of operations, then you can't use that order of operations. We can only use order of operations which give the right answer (noted that you ignored my point about 490 vs. 77 - you keep ignoring every time I point out why what you said is wrong).
It is!!
IT DOES. This is what you're failing to understand - the order of operations rules come from the definitions of the operators themselves, and only one way works. Literally the only way to change the order of operations rules is to change the operators themselves. i.e. their definitions. As long as multiplication is defined as being shorthand for addition, you'll still have to do multiplication before addition, there's literally no other way to get the right answer, hence there is only one set of order of operations rules which works - all other variations only give the wrong answer.
Ok, here you go, here is my example that you can change the order of operations and equation and still get the right answer:
2 + 3 * 4 = 14 using the order of operations [parenthesis, multiplication, addition].
2 + (3 * 4) = 14 using the order of operations [parenthesis, addition, multiplication].
There, two different orders of operation, the same answer.
Edit:
I found your counter example to this. You changed my equation, so of course it is going to be wrong.
If I changed your 2 + 3 * 4 to (2 + 3) * 4, then then your answer would be 20 and that would be "wrong". So I feel it is not a fair attack on my argument.
Edit Edit:
Again I feel like we are stuck in this loop of the right answer is 14 because that is what the order of operations give us and the order of operations is correct because it gives us the right answer of 14. This is circular logic. Nothing to be ashamed of. It's an easy trap to fall into. But it isn't a good argument.
But they're the same order of operations - you didn't do multiplication last in the second example, you did it first, because it was inside brackets.
In terms of BEDMAS...
2+3x4=2+12=14 M A
2+(3x4)=2+12=14 B A
Same order of operations rules! This is what I keep saying to you - there's no way around it! We didn't choose it, it's a law of nature. The only thing we chose is how to write it. It's the same with the Laws of Physics - they are laws of nature, and we just chose how to write them.
No, I didn't. I simply substituted addition for multiplication, as per the definition of multiplication as shorthand for addition, which in the previous comment you weren't contesting. Analogy, if you wrote 2, and I substituted 1+1, then that doesn't change the answer because 1+1=2. In the same way, 4x10=4+4+4+4+4+4+4+4+4+4
You said...
And so I did the Maths. We know, by definition 4x10=4+4+4+4+4+4+4+4+4+4, therefore I can swap those around with each other and it doesn't change the answer. So...
3+4+4+4+4+4+4+4+4+4+4+7=50, which does not equal 77! The answer is wrong, because the answer is, you know, wrong.
No, because adding brackets around addition does change the answer, because now you're doing the addition first, because it's inside brackets. (2+3)x4 does equal 20, and 2+3x4 does equal 14 - they are 2 different equations, and have different answers. You changed the answer when you added the brackets to say "do this addition first instead of the multiplication".
NO, because that's what arithmetic gives us - nothing to do with order of operations.
Here it is on a number line (no order of operations involved at all)...
And now, since we already know that the answer is 14, we can deduce the order of operations rules needed to make it so... which is multiplication before addition, and that is because multiplication is a shorthand form of addition! There are no other order of operations rules which work, only this works.
No, they're not the same order of operations. If I left out the parentheses the answer would have been 20 instead of 14. Stop assuming my example are incorrect or I have made some kind of error.
Listen I have to bow out of this conversation. I haven't found any of your arguments relevant let alone convincing. And every time you reply, you seem to intentionally miss any point that I'm making while being snarky and insulting. It's extremely frustrating to me.
Seriously, I don't know if this is sunken cost fallacy issue that you're having. Or if you're some kind of AI designed to maximize my frustration.
I'm sorry I have to end this conversation, but there other things I'd like to focus on in my life.
I wish you well.
No it wouldn't. B E D M A S. I even showed you on the number line why it's 14 (which you've ignored). No wonder you don't understand what I'm talking about if you think the answer is 20.
There's no assumption - I'm a Maths teacher. If you think the answer is 20 then you did make an error.
No, just trying to show you how Maths works. Some other people thanked me.
Did you get that answer from the Windows calculator? That's a bug in "Standard" mode. You need to put it in Scientific mode to get the right answer (I guess no-one has noticed that the "standard" mode is wrong, cos no-one uses it usually).