“A common mistake is to think division is prioritised above multiplication”

That is what I said. I said it’s a mistake to think one of them has a precedence over the other. You’re arguing the same point I’m making?

Most recommended cameras are from China unfortunately. While I would prefer to not support them economically, they seem fine security wise.

No Hikvision from Amazon, good shout as I was looking at some of them there.

Oh, that might prove a bit difficult on a Linux machine. I guess I’ll have to borrow my room mates computer :P

Thanks for the shout about Frigate’s documentation. There’s a lot of good information on there!

100% with you. “Left to right” as far as I can tell only exists to make otherwise “unsolvable” problems a kind of official solution. I personally feel like it is a bodge, and I would rather the correct solution for such a problem to be undefined.

I fully agree that if it comes down to “left to right” the problem really needs to be rewritten to be more clear. But I’ve just shown why that “rule” is a common part of these meme problems because it is so weird and quite esoteric.

Except it does matter. I left some examples for another post with multiplication and division, I’ll give you some addition and subtraction to see order matter with those operations as well.

Let’s take:
1 + 2 - 3 + 4

Addition first:
(1 + 2) - (3 + 4)
3 - 7 = -4

Subtraction first:
1 + (2 - 3) + 4
1 + (-1) + 4 = 4

Right to left:
1 + (2 - (3 + 4))
1 + (2 - 7)
1 + (-5) = -4

Left to right:
((1 + 2) - 3) + 4
(3 - 3) + 4 = 4

Edit: You can argue that, for example, the addition first could be (1 + 2) + (-3 + 4) in which case it does end up as 4, but in my opinion that’s another ambiguous case.

So let’s try out some different prioritization systems.

Left to right:

(((6 * 4) / 2) * 3) / 9
((24 / 2) * 3) / 9
(12 * 3) / 9
36 / 9 = 4

Right to left:

6 * (4 / (2 * (3 / 9)))  
6 * (4 / (2 * 0.333...))  
6 * (4 / 0.666...)  
6 * 6 = 36

Multiplication first:

(6 * 4) / (2 * 3) / 9  
24 / 6 / 9

Here the path divides again, we can do the left division or right division first.

Left first: 
(24 / 6) / 9  
4 / 9 = 0.444...

Right side first:  
24 / (6 / 9)  
24 / 0.666... = 36

And finally division first:

6 * (4 / 2) * (3 / 9)  
6 * 2 * 0.333...  
12 * 0.333.. = 4 

It’s ambiguous which one of these is correct. Hence the best method we have for “correct” is left to right.

The issue normally with these “trick” questions is the ambiguous nature of that division sign (not so much a problem here) or people not knowing to just go left to right when all operators are of the same priority. A common mistake is to think division is prioritised above multiplication, when it actually has the same priority. Someone should have included some parenthesis in PEDMAS aka. PE(DM)(AS) 😄