That’s because (strictly speaking) they aren’t teaching math. They’re teaching “tricks” to solve equations easier, which can lead to more confusion.
Like the PEMDAS thing that’s being discussed here. There’s no such thing as “order of operations” in math, but it’s easier to teach by assuming that there is.
Edit: To the people downvoting: I want to hear your opinions. Do you think I’m wrong? If so, why?
The “why” goes a little further than that.
In actuality, it’s because of fundamental properties of operations
a + b = b + a
a×b = b×a
(a + b) + c = a + (b + c)
(a×b)×c = a×(b×c)
a + 0 = a
a×1 = a
If you know that, then PEMDAS and such are useless because they’re derived from those properties but do not fully encompass them.
Eg.
3×2×(2+2) = 3×(4+4) = 12+12 = 24
This is a correct solution that is improper if you’re strictly adhering to PEMDAS rule as I’ve done multiplication before parenthesis from right to left.
I could even go completely out of order by doing 3×2×(2+2) = 2×(6+6) and it will still be correct
Oh yeah, that’s a fun one.
Where I live, this would be considered juxtaposition, at least by uni professors and scientific community, so 2(4-2) isn’t the same as 2×(4-2), even though on their own they’re equal.
This way, equations such as 15/2(4-2) end up with a definite solution.
So,
15/2(4-2) = 3.75
While
15/2×(4-2) = 15
Usually, however, it is obvious even without assuming juxtaposition because you can look at previous operations. Not to mention that it’s most common with variables (Eg. “2x/3y”).
Pre-ordering physical goods is fine, especially if you expect a price hike and supply limitations after launch. I wouldn’t, but I can see how it would make sense.
It’s the digital goods that make no goddamn sense to buy before they’re out. They’re not limited in supply, and their return window is often too small.