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Spadeninja t1_iyc313a wrote

Reply to comment by BurnOutBrighter6 in ELI5 why we first multiply, then add by TheManNamedPeterPan

The thing that is confusing to me though is that math is precise - especially when considering massive undertakings like space flight for example

There are laws of physics and math… so if the reasons why the order of multiplication vs addition (despite leading to potentially VASTLY different conclusions) are somewhat arbitrary… why does it still work?

The example in the original post lead to two different answers, and that was an extremely basic example.

How does this work with hundreds of different calculations?

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BurnOutBrighter6 t1_iyc3kd5 wrote

The math itself is fundamental. It would work no matter what convention we chose. The only arbitrary thing we're deciding on here is how to WRITE math so other humans know what you mean when there's more than one possibility.

(more than one possibility for what math you're trying to describe, NOT more than one way that the math itself could go!!!)

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Spadeninja t1_iyc3ukk wrote

But we arrive at two different answers depending on which path we choose

Like if it was a math test should the teacher mark both correct?

Sorry just trying to make sense of how both answers are right when there should be a right answer you know what I mean?

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BurnOutBrighter6 t1_iyc4yuq wrote

Both answers aren't right. On a test only one of those is right, and one is wrong. When you write:

1+2x3

That means "multiply two x three, then add one". There is only one right answer to this. It's 7. 9 is wrong.

If what you actually meant was add 1+2, then multiply by 3, than you have to write it as (1+2)x3, and then the only right answer is 9.

The rules we're talking about here are only about how to write the math so that it means what you intend it to mean (like multiply 2 by 3 then add 1, vs add 1+2 then multiply by 3). But for whatever you write, there's only one right answer.

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Spadeninja t1_iyc5chh wrote

Yes I get that

The question is though

When you have thousands of calculations, again in the instance of like a rocket launch, both are correct as long as everyone is on the same page?

And is the order between adding and multiplying is mostly meaningless as long as everyone is using those same calculations?

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John_Vattic t1_iyc64td wrote

In your example, you're talking about if the 'agreed language' of math was different, the other answer would be correct. But, if the required answer for this scenario was 7, the actual calculation would be written differently.

It's like if you have a room full of people speaking English, and one dude who only speaks French. It's not that French is wrong, but they're not going to be understanding each other.

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Spadeninja t1_iyc89h3 wrote

Right……

But like if the math adds up then what makes that one French person wrong?

Not sure what point you think you made mate

My question was about the math not about culture

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John_Vattic t1_iyc8ya7 wrote

Nothing at all makes the French person wrong, if the math adds up. I'm not talking about culture at all, it's just an example, like launching a rocket mentioned earlier in the thread. You seem a little angry, you ok?

To put it another way, forget about the equation. The "required" answer to launch the rocket in the example at the start of this thread is 7, not 9. Could we conceivably write and read math in a different order? Yeah absolutely, but if we write math the same and two people read it differently, then there's too much rocket fuel and it explodes on launch. That's why we have a standard for reading back these equations so that we can all get to the same answer.

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