8 / 2 (2 + 2) =

jimhorner said:
What your actually doing here is incorrectly evaluating the multiplication and division right to left instead of left to right.
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Maybe I got the idea from this guy? :tongue:

jimhorner said:
The teacher said "learn and memorize this:"

Order of precedence:
1...
2...
3. Multiplication and Division right to left
4. Addition and Subtraction right to left
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dtuuri said:
The expression 2(2+2) is welded together in my mind as a single value because of some long-ago math training. I'm not alone in this thread on that point, although feeling a bit abandoned at the moment. I'm looking for the source of it. You all miss the point that we understand what you do these days and why you do it, but it doesn't make it easy for us old-timers who learned these rules before they invented battery calculators.
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Well, as I mention previously, my 91 year old father and 86 year old mother, both of whom I would classify as old timers, correctly evaluated the original problem as 16 with only a few second to mentaly compute the result. I suspect you just learned it wrong early on, and the law of primacy is preventing you from accepting that. 2(2+2) is not accepted as being welded together by people who were taught correctly.

To me, this is like saying that in my mind the Sun revolves around the Earth or that the Earth is flat. I'm doing no harm in believing that, but neither are true.
 
dtuuri said:
The expression 2(2+2) is welded together in my mind as a single value because of some long-ago math training. I'm not alone in this thread on that point, although feeling a bit abandoned at the moment. I'm looking for the source of it.
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I suspect the source is, like @Rene , the teaching simply wasn't correct. Rene was taught much later than you. I bet that, somewhere in the USA, they still teach that Columbus "discovered" the Americas. Or the teacher simply used the book with its typesetting.

dtuuri said:
That's a pretty interesting history, but I suspect the author isn't much fun at parties. Left-to-right is non-controversial, so I don't see the need to discuss it.
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The history is important since it shows that the order of operations for a linearly written equation was established since 1912, if not earlier. It should have been taught to you by 1961.
dtuuri said:
They didn't have them when I first took algebra in 1961, at least in high schools. We were more concerned (well, the teacher was) with historical math principles.
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Maybe math principles from the 1800s?
 
jimhorner said:
Oh my goodness. Wow, I really goofed there, didn't I? Huge oops!
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It's ok, happens to the best of us. :)

I think I found out where you're going wrong. You're using PEMDAS not PEJMDAS! It seems that "juxtaposition" multiplication is supposed to be done first; thus, the answer is 1. See: https://en.wikipedia.org/wiki/Order_of_operations
PEJMDAS is a more sophisticated mnemonic for higher math. I must've learned that rule without knowing it.
 
Aha! It isn't the whole world that wants to change to only PEMDAS rather than the long-time PEJMDAS, it's the North American teachers only! I can't help but think Rene sounds like this girl:

Any N-A teachers in this thread?
 
Good morning, class! Did everybody finish their homework assignments? What a lovely treatise, wasn't it? And what a lovely girl, too. I watched it twice with closed captioning so I wouldn't miss a single word.

So, why on earth would the teachers in North America want to dumb down an ordering of math operations that I and others, apparently, were taught in Algebra 101 some 50 years ago? They lobbied calculator manufacturers to drop the "J" step from PEJMDAS. Now, after training multitudes of scientists, engineers and teachers to a different order of operations, there is a mix of calculators on the market (and online) giving different results to the same problem. Nice work, teachers. WTF were you thinking, huh? Kudos to Casio for resolving the issue.
 
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Hmm. Microsoft's calculator is PEMDAS too. I have to wonder if that's why my classic, recently depreciated, Windows calendar events won't migrate over to the force-fed new Outlook calendar. Was Windows Calendar made with PEJMDAS and new Outlook with PEMDAS?

And then there's Boeing. Not far from Microsoft's headquarters, I think. Do they use Microsoft's elementary school level PEMDAS calculators to design newer advanced aircraft while the older models used PEJMDAS? Maybe they figure 8 rivets per 16 square feet where older engineers got 8 per square foot? :dunno:
 
dtuuri said:
Aha! It isn't the whole world that wants to change to only PEMDAS rather than the long-time PEJMDAS, it's the North American teachers only! I can't help but think Rene sounds like this girl:

Any N-A teachers in this thread?
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Not a teacher, but as an 80s-era math/algebra learner, it was PE(J)MDAS in our district and likely state.

The rationale was unless a space exists before the parentheses, the leading number was part of the parenthetical equation. I seem recall there being some type of relationship to first, outside, inside, last method of binomial distribution.

But I’m digging deep in the memory banks here because I haven’t had math theory since learning RADAR math in 1996. Don’t ask when the last time I used that was, but it was a much more applicable concept to my daily life than algebra and trig has been. At least due to my math teachers who carried on how the correct answer to a trig problem could not be found without showing the proof.

The problem came to a head when I got back a math test graded “0” with zero incorrect answers. That’s when that teacher learned there’s more than one way to skin a cat and I learned how absolutely hard headed I could be. The written directions on the test did not specifically require “show your work to include the proof”, it only said to choose the correct answer among those provided.

Test was supposed to be SCANTRON graded, but the teacher didn’t like running the cards AND reviewing a separate worksheet, so she handed out just the worksheet.

Long, irrelevant story short, I was given the opportunity change teachers, retake the test, and get full credit. While the drama played out, I got six weeks off from extracurricular activities because the I had failed the class due to the test. It was then I really, really understood the school system wasn’t as interested in students learning as much as it was about cementing teacher authority.
 
TCABM said:
. . . . It was then I really, really understood the school system wasn’t as interested in students learning as much as it was about cementing teacher authority.
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FIFY :)
 
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