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Math Help - Subtracting Integers - sea level difference

  1. #1
    Junior Member Euclid Alexandria's Avatar
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    Question Subtracting Integers - sea level difference

    From the book: "If the elevation of Lake Superior is 600 feet above sea level and the elevation of the Caspian Sea is 92 feet below sea level, find the difference of the elevations."

    My answer: 600 - (-92) = 600 + 92 = 692 ft

    Am I correct? This seems very obvious to me, but I'm just double checking.
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  2. #2
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    Quote Originally Posted by Euclid Alexandria
    My answer: 600 - (-92) = 600 + 92 = 692 ft

    Am I correct? This seems very obvious to me, but I'm just double checking.
    Hello,

    you've got it. It's perfect: Congratulations!

    Bye
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    Junior Member Euclid Alexandria's Avatar
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    Thanks!
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  4. #4
    Newbie Waveform's Avatar
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    Question

    Hi Iím kind of new to this stuff, I never had algebra before.
    Can I just ask a quick question?

    If you know lake-A is 600+Feet above see level and another lake is -92 feet, why doesnít algebra just say 600 + 92 = the difference?

    What I mean is: 600 Ė (-92)
    Is the same as saying 600 + 92.

    So I guess what Iím asking is, what is the advantage or better yet how dose it relate in the real world? Sorry for the amateur question but Iím just trying to keep my thinking in line. Some of these sound too easy which is what freaks me out, because I know something crazy is right around the corner and I know that all these principles will matter once I start getting into this stuff. Can someone please explain why Algebra problems are twisted or worded different, all for the same answer? What would be a real would example for this?

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  5. #5
    Grand Panjandrum
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    Quote Originally Posted by Waveform
    Hi Iím kind of new to this stuff, I never had algebra before.
    Can I just ask a quick question?

    If you know lake-A is 600+Feet above see level and another lake is -92 feet, why doesnít algebra just say 600 + 92 = the difference?

    What I mean is: 600 Ė (-92)
    Is the same as saying 600 + 92.
    The problem is intended to show that subtracting a negative number is the
    same as adding the corresponding positive number. So it is obvious to you
    that the difference in heights is 600+92, and this illustrates that 600-(-92)
    is the same thing.

    At some point you will see the general rule

    x-(-y)=x+y

    and this problem just shows why we want the rule that minus times minus
    as used here is plus.

    RonL
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  6. #6
    MHF Contributor Quick's Avatar
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    I realize that this is really late.

    I would like to point out why in algebra you say 600-(-92)
    it is because in moderately low to highly advanced math you are NOT allowed to use logic, only formulas. Therefore, I would say the formula for solving this problem is a-b=c and then I would substitute the values into this equation (600)-(-92)=692

    Another reason: when you start to get into bigger equations, you will have to use the cumulative property of addition and other properties...
    an example:
    2x^2-3x-x^2+5x\quad\Rightarrow\quad2x^2+(-3x)+ (-x^2)+5x\quad\Rightarrow\quad2x^2+ (-x^2)+5x+(-3x)\quad\Rightarrow\quad x^2+2x
    Last edited by Quick; July 11th 2006 at 06:46 PM.
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