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Simplifying equations. Orders of operation.

  1. Sep 16, 2012 #1
    Simplify the following expression.


    My answer was 20 and it was wrong.

    When i look at this i see, 2 plus 1 times 2 minus 4 times 6
    The part im getting wrong is the minus, which in this case means a -4 instead of a 4.
    I dont understand how you can you tell the difference ?
    My only conclusion is that since this is a order of operations module, that this doesnt really exist outside of the module, that its just a example for learning ?
    Or maybe since its saying to simplyify the expresion, that right there is telling me that im not going to add or subtract some how ?

    Thanks for any advice in advance
  2. jcsd
  3. Sep 16, 2012 #2
    This should do it :biggrin:
  4. Sep 16, 2012 #3
    The generally accepted order of operations are BIDMAS (or BODMAS, same thing), which is:
    Brackets, Indicies, Division and Multiplication, Addition and Subtraction.

    So, brackets are computed first, then indices (powers), then division and multiplication have equal priority, and are done left to right, then addition and subtraction, which also have equal priority, are done left to right.

    In real life, nobody should write anything as ambiguous as this, because it just causes problems. (2 + (1 × 2)) - (4 × 6) would be a far better way to write it.
  5. Sep 16, 2012 #4
    Ahh ok i get it now.

    Couldnt wrap my head around it or a second. Thank you. :)
  6. Sep 16, 2012 #5
    I don't get it. Why is given expression ambiguous and why is your answer wrong?
  7. Sep 16, 2012 #6


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  8. Sep 16, 2012 #7
    I still don't get it. I'd bet everything that the expression evaluates to -20.
  9. Sep 16, 2012 #8
    It does = -20

    What I was doing was subtracting wrong.

    I think my failure came from forgetting that you always go left to right, no matter what. I think I automatically subtracted 4 from 24 when what it's really saying is 24 from 4. In other terms, I was thinking 24-4 and it's plainly saying 4-24.

    Yes, I'm very certain this is what happened. But to acabus point, had there been a parentheses around the 4x6 it would have been a little more clear. Which makes me feel better lol.

    It's amazing all the reflexive math I'm running into. I never dealt with negative numbers in the jobs I've had, so when I see numbers like that, if I'm not slowing my mind down and thinking, I instinctively subtract small numbers from big numbers. Embarrassing to admit, but what can I say, I grew up how I grew up. I'm just glad I get a chance to advance my math to a functional level now. I just wish 15 year old me knew how cool math is. No one told me I could use it to fly to the moon or mars, or understand how the universe works, how planets and stars move in the sky. I might have paid more attention if they had.

    Hope that helps.
  10. Sep 16, 2012 #9

    Thank you, that helped me understand acabus better. And a lesson for any expressions I right myself.
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