re: This math problem is clearly only for geniuses...

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Am I explaining clearly? I often seem to fail at that

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I fully understand what you are saying.

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The key in understanding this is that the equation is written to be solved left to right so the expectation is, assuming all parenthesis and exponents have been resolved, the operation indicated will be performed on the next single number.

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I have however never actually been taught this. All the math needed to get a mechanical engineering degree plus additional 4000 level math classes writing proofs to fulfill my technical electives and I never have looked at a problem as being solved left to right. Not once. If you had to differentiate between what went first, parenthesis were used. Never was a problem left up to the "left to right" rule. I think this is just something taught at some (and it may be a lot) grade schools. But I was not familiar with it until here. Yes I've used PEMDAS, but not with the left to right rule added on. And if you just use PEMDAS, I can get different answers to my original problem.

In order to substitute that, you have made an assumption already that division is taking place. You are putting your own parenthesis in there. Maybe it's cleared if written as below

3x8÷2x4=

The division sign is tied to the 2 just as much as the multiplication sign is. It's up to you to determine which goes first if you ignore left to right. You have made assumptions and assigned an order of operations to make your argument.

3x8÷2x4=

Google says "48" - you have to go in sequential order with the MD part of PEMDAS. If you hop around, as you suggest, you are inserting parenthetical operators where none are specified.

Addition and subtraction does not matter and will not alter the final result. Doing so with MD part can.

But you would never resolve addition or subtraction before multiplication/division under PEMDAS.

ETA: The problem I believe in this one is the haphazard use of / as a division operator. While it is "okay" for a shorthand, it is improper if it leads to confusion - for example, if 1/2 is meant to represent the division operation of 1 divided by 2 - and not a fractional value within the equation - it's fine. Otherwise, when representing a division operator, it should be confined to ÷ to eliminate that confusion.

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you have to go in sequential order with the MD part of PEMDAS. If you hop around, as you suggest, you are inserting parenthetical operators

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Again, this is with the assumption that there is a left to right rule. I'm assuming that's how Google's code is written as well. I'm just stating that I've never once been presented a math problem (that I can remember) that this came up. Parenthesis were there. If I had to write the problem, I included the parenthesis. This does probably go back to the engineering side of me. One, the problem always modeled something, so you had a reason to answer certain parts first. Two, most division is done with a horizontal line dividing the arguments so you look at them as separate.

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As written, you have to make an assumption somewhere.

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That was the point of the original post. Someone had said that it didn't matter which way you did the operations with multiplication and division, it will always come out the same. I was just proving that wrong.

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Again, this is with the assumption that there is a left to right rule.

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Well there is. And if you're using something else -as industry practice, SOP, or what have you, then it better be damned clear or we're operating in an environment of "no rules".

I've certainly never seen the / take precedence over X or * - but I can see where as it represents a fraction (which, itself is a representation of a internal division operation and expressed as such) as opposed to actual division, it can present a risk to the consistency of the output.

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I thought it was an obvious troll A successful one apparently

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6 replies and counting

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Then how come I've never seen it?

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Can't help you on that one, baw.

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If it is such a well known rule, why has every problem I've ever answered included unnecessary parenthesis.

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Belt and suspenders. I certainly wouldn't call your parenthesis "unnecessary" - if it eliminates confusion, I think my post was clear - we should go with the less ambiguous whenever possible. In the absence of that - if it makes a difference, I think we have to assume the drafter intended PEMDAS and left-to-right to be followed in the absence of other or more specific markers.

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If this is a rule, then so many text books could have saved some ink a removed the parenthesis since left to right was good enough.

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Meh. Seems like you're melting a little bit now. I wouldn't worry too much about it.

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College level classes will not leave this up to a right to left rule. Why are so many equations poorly written when they could be reorganized and never need parenthesis in the first place since left to right would take care of an ambiguity.

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Yeah - maybe more than a little melting here. Good luck with it my brother - I don't think we're all that far apart.

17:38

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My local McD's is terrible. I ordered a hamburger with only shredded lettuce. I got exactly that--a bun with only shredded lettuce (no "meat").

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I've done this before when i worked at mcdonlads. customer in the drive thru was being belligerent with the cashier in the drive thru window. he wanted a Quarter pounder, only ketchup. She asked would he like cheese since its a common issue(people saying only one item and not wanting cheese, or people saying only one item and we not put cheese on there and they wanted it, so we just made it our policy to ask to ensure highest customer satisfaction.) Well this douche cusses the girl out("bitch is you retarded. i said i only want fricking ketchup stupid bitch") and i hear it because i have the headphones on as well. So i gave him just what he asked for, quarterpounder bun, ketchup, bottom bun. It was right around closing so by the time he realized it, we were closed.