system
Given the following post, respond as if you're commenting on Reddit:
human
eli5 6÷2(2+1)=? 9 or 1 and why?

This debate has been messing up with my mind, I find 1 whereas some of my friends find 9 as well as the professor, yet I’m sure of myself. Could y’all explain me how is it 1 or 9 and why.
gpt
These kinds of problems that you see on Facebook are intentionally vague, and no proper mathematician would write them out this way. 

Everyone can easily agree that the `2+1` in the parentheses evaluates to 3 before anything else, but then it's the matter of whether or not that 3 is multiplying the 2 before the division, or the 3 after the division.

Part of this is that, in different parts of the world, we might learn `PEDMAS` or `PEMDAS`, with the Multiplication and Division switched in order. In truth, it really doesn't matter because they are the *same* operation, just in inverse. Dividing by 2 is the same as multiplying by 0.5, after all. This is made worse by the fact that a lot of people just learn the procedural parts of math, and don't learn why things work the way they do and don't have any critical thinking.

A proper mathematician would write `(6/2) * (2+1)` or `6 / (2 * (2+1))`, which are completely unambiguous.