# Why can't Scientists and People Understand PEMDAS?

1. Sep 13, 2013

### ZeroPivot

I mean if a normal person doesnt understand it thats fine but when scientists are wrong about it it drives me insane

watch this vid from this physicist:

it makes me want to murder kittens!!!

LEFT to RIGHT, addition substraction are interchangable same thing with multiplication and division.

it makes me sooooooooo angry when they think or assume that addition has precedensce over substraction why are people so SLOW in the head and this is suppose to be a physicist!!!!!

Last edited by a moderator: Sep 25, 2014
2. Sep 13, 2013

### HallsofIvy

Scientists, in general, do NOT post on "youtube". Whoever posted that was clearly NOT a scientist so your outrage, while clearly deserved, is misplaced.

(And please don't take it out on the kittens!)

3. Sep 13, 2013

### symbolipoint

Different kinds of minds. Some catch-on very easily and others do not. Order of Operations and the meanings of grouping symbols are mostly intuitive for me. I would seem to be sharing your advantage for this about Arithmetic skills.

Last edited by a moderator: Sep 25, 2014
4. Sep 13, 2013

### caper_26

What is your take on grouping symbols, ie:
2(2+1) ÷ 2(2+1) ?

Do the parentheses and factor of the inner terms take priority over division?
Cheers.

5. Sep 13, 2013

### D H

Staff Emeritus
So he got it wrong. How many times have you been told not to believe everything on the internet? What did your kittens do to deserve abuse because someone said something wrong on the internet?

Multiple things wrong, actually. I was dubious that Frank Reich could have made a video that has a crackpot title. But yes, that's exactly what he did. I stopped watching when he got to the point of saying "a mathematician will tell you that 8-2+1 is really 8+(-2)+1." No, she won't. Not if she knows her mathematics. What if the domain is the natural numbers where there is no such thing as -2?

Strictly speaking, no. That's 9. You obviously want the answer to be one. Or something else other than 9.

IMO, an even better answer is the answer your doctor gives you when you complain "Doctor, it hurts when I do this."

"Well don't do that then."

Don't intentionally try to create ambiguous expressions. Use parentheses, or use a nice typesetting system such as TeX to create unambiguous expressions.

Note that this means we physicists should stop using expressions such as $1/(e^{h\nu/kT}-1)$.

Last edited by a moderator: Sep 25, 2014
6. Sep 13, 2013

### caper_26

What is 4(a+b)³ ÷ 2(a+b)² ??

7. Sep 13, 2013

### D H

Staff Emeritus
If you are here to argue that implied multiplication has a higher priority than explicit multiplication or division, it doesn't.

http://www.wolframalpha.com/input/?i=4(a+b)^3+/+2(a+b)^2

Do not take this thread off topic by making that argument.

8. Sep 13, 2013

### Turion

I can't believe people are getting all upset over arbitrary rules.

And you guys are calling him a crackpot over it! Over arbitrary rules...

9. Sep 13, 2013

### D H

Staff Emeritus
Are they arbitrary? Of course. Without those rules the expression 1+2*3 would be ambiguous. We would have to use parentheses everywhere to remove the ambiguity. Those arbitrary rules exist to let us get rid of some of those parentheses. Even though they're arbitrary, those rules must be standard to keep ambiguity from creeping in.

Or we could use prefix or postfix notation. There's no confusion there. We're stuck with infix, however, so we either need parentheses or arbitrary rules that enable us to eliminate some of the parentheses.

This is not Reich's shining moment. This video is no different than someone who starts a thread at this site entitled "Relativity is wrong!".

10. Sep 13, 2013

### symbolipoint

The each grouped expressions is first understood as number separate from all other numbers in the entire full expression and no confusion is found. That is the meaning of using grouping symbols. They give a boundary, a symbolism boundary to express a number or expression of numbers separately from other numeric symbols near it.

I myself do have some faults in my PEMDAS knowledge and I might make a mistake in handling your expression given there. This is why I usually will not use the division symbol which you show. I would use rational expressions when appropriate and NOT the division operator with the top & bottom dot.

11. Sep 13, 2013

### caper_26

Thanks for your thoughts on that parenthetical grouping topic. Obviously, discussion in sane form is not really welcome here as a few of my posts after that were deleted... a perfectly accepted way of using the rules of simplification, and some other discussion points on order of operations to the OP. It seems a nerve was touched and they felt a need to pull internet rank, lol. And then of course, they go make their own points, as if some almighty authority on the discussion, while mine get deleted. Anyway, best regards to you.
Cheers pal.

12. Sep 13, 2013

### TysonM8

If you watched the whole video, you would notice that at the end he says the order of operations is not technically wrong, but morally wrong.

13. Sep 14, 2013

### verty

That's even worse. The order of operations is what it is, learn it, use it, the end.

14. Sep 14, 2013

### arildno

A guy is certainly a crackpot if he opposes established arbitrary rules in favour of other arbitrary rules that have no advantage over the already established rules.

Established reality is a weighty matter not to be pushed aside arbitrarily.

15. Sep 14, 2013

### ZeroPivot

We even have people here that dont understand pemdas where are they coming from????

16. Sep 14, 2013

### D H

Staff Emeritus
This thread is causing silly arguments and is getting people in trouble.