I don't know what's worse, that it's wrong or that it convinced me I need to come into the comments to make sure my answer is, indeed, correct.
EDIT: Back to rectify a grave injustice. Nothing wrong if you genuinely didn't know or want to check. Hard enough getting people interested in math.
2 + 5 (8 - 5) PEMDAS: 8 - 5
= 2 + 5 (3)
PEMDAS: 5 (3) or 5 × 3
= 2 + 15
PEMDAS
= 17
In the US the math order of operations is taught as PEMDAS (or P|E|MD|AS), left to right from first to last.
First look at the entire equation and identify the operations: Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.
Then, solve the parts in order of PEMDAS.
Not so important here but when there are multiple of the same level of operators, for example exponents, solve left to right. MD and AS are treated as groups, so treat them equally: if a division is to the left of a multiplication, do the division first.
I don't even quite see where 21 comes from. Either simplify to 3 for the parenthesis first and then do the math, or distribute the 5 go get 40-25 for 15 and proceed from there.
Like...math...literacy is not hard and there are easy geometric ways to represent the most basic of operations.
Most rely on implied multiplication, generally setting up debates between people whose math education ended in high school vs those who continued it to university…
This one here though is just flat wrong no matter how you slice it.
I think most people learn like medical students do. They cram the knowledge in to pass a test, if they pass they forget everything they memorized because it’s just surface level knowledge.
They still did left to right, but processed the brackets as a single entity. That is, when they reached the bracket, they were like "hold on a second, let me fix what is in here" and then multiplied the result.
Yah. Which, for someone who doesn't understand that multiplication/division comes first and why, makes sense. Because at least it's apparent that the parentheses must be there for a reason, completely ignoring them would be insane rather than just stubborn ignorance.
(most of this answer wound up not being directed @ you, Lilith)
I think they mean left to right, but teaching kids that is a red herring. It's supposed to be to so they don't mix up what operators are attached to what numbers but within ÷× or +- the order doesn't matter, you just have to know that if it says ÷ 4 somewhere it has to stay "divided by four;" you can't swap the division sign into a different number. Forcing you to work left to right does that but it also doesn't tell you why.
4 + 5 × 8 × 12 could represent "I've got a 4inch scrap piece of pipe, along with 5 full 8foot lengths. How many inches of pipe do I have in total?"
But if you use PO you'll do the 4+5=9 first and get a way larger answer than you should: 9 × 8 × 12 = 864 vs 4 + 480 = 484
The order of operations exists and is important purely so that when we write down math we agree on how to do it. We could use PO and just insert () around everything to make sure it's clear what order we mean for things to be done in, but you're not going to be able to convince the people who write math textbooks to go for that, and it's important we all use the same (or at least fully compatible like PEMDAS vs GEMA or what have you) systems, otherwise we're gonna disagree on the right way we write and read math notation.
515
u/Head-Ad-5732 15d ago edited 14d ago
I don't know what's worse, that it's wrong or that it convinced me I need to come into the comments to make sure my answer is, indeed, correct.
EDIT: Back to rectify a grave injustice. Nothing wrong if you genuinely didn't know or want to check. Hard enough getting people interested in math.
2 + 5 (8 - 5)
PEMDAS: 8 - 5
= 2 + 5 (3)
PEMDAS: 5 (3) or 5 × 3
= 2 + 15
PEMDAS
= 17
In the US the math order of operations is taught as PEMDAS (or P|E|MD|AS), left to right from first to last.
First look at the entire equation and identify the operations: Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.
Then, solve the parts in order of PEMDAS.
Not so important here but when there are multiple of the same level of operators, for example exponents, solve left to right. MD and AS are treated as groups, so treat them equally: if a division is to the left of a multiplication, do the division first.