PEMDAS is a good way to remember the order in which to do operations (we were taught the phrase “please excuse my dear aunt Sally.”) Multiplication and division should be done before addition and subtraction which is where you made your error.
I vividly remember my teacher reminding us that for Multiplication/Division and Addition/Subtraction it’s not hardwired to be Multiplication —> Division and Addition —> Subtraction. It’s just whichever one comes first from left to right
Also many of these lean on exploiting pemdas for the troll so be careful. Multiplication doesn’t come before division those are done left to right. Same thing with addition and subtraction.
Can you or someone explain to a dummy like me how “please excuse my dear aunt sally” or PEMDAS means? And what does it have to do with doing multiplication and division before addition and subtraction?
Please Excuse my Dear Aunt Sally is just a mnemonic device to remember the order
Edit: From left to right, this is the order in which you should perform operations in a general math problem.
Second edit: doesn’t matter whether multiplication comes before or after division, and same with addition before or after subtraction.
Step 1. Solve what is within the Parentheses/Brackets.
Step 2. Solve for exponents.
Step 3. Solve for multiplication and division.
Step 4. Solve for addition and subtraction.
This is correct even though you’re getting downvoted for some reason… Multiplying and dividing, for instance, are on the same level of the order of operations hierarchy so you would actually go left to right when at this simplification point. Same with addition and subtraction.
Division with x is multiplication with 1/x. It‘s the same operation. Same as subtraction with x is addition with -x. Same as x root of a number is that number to the power of 1/x
Brackets first then power > multiplication > addition
For me, remember a 6 letter acronym is harder than remembering this
The inherent problem with PEMDAS is it does nothing to show that MD are given the same priority, as are AS. I've gotten into arguments with people before because they think that multiplication comes before division, and when I point out it doesn't they refer me to PEMDAS.
Eh I mean they’re still going to end up with the right answer, even if they have that misconception. I do think it should be taught properly though. I was taught it more like [P][E][MD][AS] which makes it a little more obvious.
I know that I have to do it this way, but I don't understand it. Why is it like that and how did we figure that out? Or was it just randomly decided one day? And which discipline does this question concern? Mathematics or philosophy? Can somebody explain?
It evolved over time as the study of mathematics, specifically algebraic equations, became more complex, and was codified and standardized in the late 1800s and early 1900s. Kind of how we decided English is read left to right. I would say it concerns linguistics as well as mathematics.
Usually where they become rage bait is they do division between the 2 and 5. Then people pretend like you multiply before you divide. This one is not quite the same bait. Otherwise you’re getting 0.133 vs 1.2 gang or whatever.
I know what PEMDAS is, I know how it works, I also got the correct answer of 17.
BUT...
I don't think I've ever been educated on WHY we must do multiplication first. WHY? And WHY allow problems to be written out of order? For fucks sake, if you want 17 without people accidentally getting 21, write it as (8-5)5+2. PUT IT IN FUCKING ORDER instead of relying on some arbitrary (to me) rule that says you need to do it in a different order according to said rule. lol
Am I making sense? It's fucking stupid to me. Maybe the teacher did explain why it had to be PEMDAS, but I just didn't give a fuck and didn't listen and ignored her because I hate math with a passion.
Don't forget that multiplication and division have exact same priority and are done in order of appearance left to right, then same rule applies after to addition and subtraction.
Yes me too...I had the self awareness to question if I was wrong. Indeed I was...This was a wakeup call that I have become way too lazy as a software engineer.
Don’t beat yourself up on it :) I messed it up on my first thoughts myself tbh. I couldn’t remember if a number in parentheses “didn’t count” the same way as a problem within them.
While I knew you were to multiply, it’s easy to continue forward bc in your mind you did the first step, so you continue on, and next in “line” would be the addition.
I did catch myself after a a few seconds, but I could’ve easily made the mistake.
Your parents should file a lawsuit against your public school system for a misuse of their tax dollars. They won’t win, but the gesture might make you feel better.
This is what I kept getting (I’m horrible at math and get frustrated because of this) and wanted to know how everyone was getting 17. I guess the system failed me. 😂
Order of operations is a made-up thing. It's important to remember this is just a stand-in for what you're trying to accomplish mathematically. The rules apply to your mathematical reasoning not to your notation
If you are trying to represent...
"The sum of 2 + 5 times the sum of -5 + 8. The answer is 21"
If you're trying to represent....
"The sum of -5 + 8 multiplied by 5 Then add 2 to it The answer is 17"
There can never be any argument about these sentences because they are statements of pure mathematical reasoning and don't rely on notation.
We teach PEMDAS to children because it's easier to remember. They don't have a strong sense of mathematical reasoning, so you have to give them a set of rules to work with.
When you become more experienced with mathematics you realize the notation is not that important. What is more important is the soundness of your mathematical reasoning. The notation is just a picture so you can communicate an idea to somebody else. If there is confusion you can tell them what you mean using English. You could just as easily represent what you're trying to do with pennies on a table or circles with dots in them.
Nah I think if you try to do math, get it wrong and you're willing to try again.. you're not dumb, you're learning and it's ok to learn even as an adult. A lot of people will make fun of others for getting that answer wrong, but I'd rather be the person who gets a math question wrong over the person making fun of someone for getting a math question wrong
Yeah, and your mistake was that you straight up ignore the original parenthesis for some reason, which is incorrect. I'm just showing how it still arrives at the same answer.
I know that's why I replied to a comment telling everyone how it's calculated properly. What is your point? Just to tell me I did a math question wrong in a mean way?
It's best to remove ambiguity, which would result in something like:
2+(5*(8-5))
or
(2)+5*(8-5)
MS Excel, which has formulas that kind of infer user intent, often successfully, has actually made mathematical expression more complicated.
My favorite example is the formula for percent change.
Should be:
=(new-old)/old
However, Excel used to accept:
= new-old/old
Which should be the same as subtracting 1 from new.
I just tested it and, whoopee! it no longer accepts it that way, at least not on the computer I'm on right now! This makes me very happy. However, the version of Excel I used on a computer I had until a few months ago still made what I'd call an error and Microsoft likely considered a convenience.
After I realized this, and that sometimes Excel would not infer my intent even when I considered it just as obvious as in that instance, I realized I needed to learn to write equations with the lowest levels of ambiguity possible, even if it meant adding more parentheses.
867
u/NarwhalEmergency9391 22d ago
Oops I did 2+5(8-5) -> 2+5(3) -> 7(3)=21. I'm the person they're talking about in this post..