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Math Help - Mental Blockage

  1. #1
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    Apr 2009
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    Mental Blockage

    Hi all,

    Been a while since I went through my Order of Operations and I have a problem that I know the answer to but I need someone to help me see why the answer is correct... if that makes sense.

    Problem is 3-4[-10-4(-5)]
    Correct Answer is supposed to be: -37

    1) I know to work inside parens first...
    2) Since there is no real work inside the Parenthesis... this is where I mess up I think... I would do Multiplication next... so I would take the -4 * -5 and get +20... correct?
    3) Next I would then take the -10 * +20... I know this can't be right.. so I try again... using only the +4 * (-5) and that gets me closer but doesn't really make sense to me because the -10 - 4 is actually a negative four right? Arrggh!
    4) So then -10 * -20 doesn't work either... please help!

    Step by step is ok... but really need the Why. Thanks in advance for your assistance and advice.
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  2. #2
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    e^(i*pi)'s Avatar
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    West Midlands, England
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    Quote Originally Posted by garms View Post
    Hi all,

    Been a while since I went through my Order of Operations and I have a problem that I know the answer to but I need someone to help me see why the answer is correct... if that makes sense.

    Problem is 3-4[-10-4(-5)]
    Correct Answer is supposed to be: -37

    1) I know to work inside parens first...
    2) Since there is no real work inside the Parenthesis... this is where I mess up I think... I would do Multiplication next... so I would take the -4 * -5 and get +20... correct?
    3) Next I would then take the -10 * +20... I know this can't be right.. so I try again... using only the +4 * (-5) and that gets me closer but doesn't really make sense to me because the -10 - 4 is actually a negative four right? Arrggh!
    4) So then -10 * -20 doesn't work either... please help!

    Step by step is ok... but really need the Why. Thanks in advance for your assistance and advice.
    I believe in step 3 you're adding -10 to +20 instead of multipying
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  3. #3
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    Joined
    Apr 2009
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    Thanks e^(i*pi)

    Yes, I see that I did make a mistake in step three... reworking now...

    Thank you,
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