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Walty_C t1_iybftk5 wrote

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

Why couldn’t you just write it 5 x 12 + 2 and solve it all left to right? Or just stick with parentheses as the operator. (5x12) + 2. Could math not be simplified in this way or would it fall apart with more complex equations?

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bovisrex t1_iybhjf5 wrote

You can and should. A large function in algebra (including basic mathematics) is in making a long problem easier to understand. The problem you wrote could also be written 12 + 12 + 12 + 12 + 12 + 2, but writing it as 5 x 12 + 2... or (5 x 12) + 2... makes it understandable at first glance. This is all that is meant by the common math problem "Simplify this equation."

Agreeing on a convention to write math problems a certain way just removes ambiguity and makes it possible for any person familiar with the relatively simple Order of Operations rule to understand any other problem written by someone. My biggest problem with the order of operations "riddles" that swarm Facebook from time to time is that they'll intentionally write them in a confusing way in order to trick people. It's the same as posting a scribbled rough draft of a paragraph and then making fun of people who misinterpret it.

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Salindurthas t1_iybms9m wrote

>Why couldn’t you just write it 5 x 12 + 2 and solve it all left to right?

Well, what if you are writing down the eggs you see, as you see them?

What if you spot 2 eggs, so you write that down, and then spot 2 cartons of a dozen, so you write that down.

Oh, dang, now you've written 2+ 5x12, and under your convention, that isn't what I meant (I've written 7x12, but I mean 2 more than 5x12).

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Or, what if you have a formula like: "D = 2*x/y + 5*z^2"

You might be working in a lab, , and your assistant tells you "I've measured x & y, they are 7 and 3.5 respectively."

You're waiting for them to measure z, and figure that you'll simplfiy your equation, and you work out the left term happens to be 4 (2*6/3.5=4).

So you write "D = 4 + 5*z^2" to keep your equations easy to read and lined up.

Oh, dang again! That isn't what you meant, you need to change the order around!

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I think it is better to have a convention where the order you write addition in doesn't matter, so that you can add things as you discover them/calculate them, rather than needing to reorder your equation every time.

You *could* do it, but I think if society did, we'd have more errors than using our current convention.

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