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Math Help - algebraic equation

  1. #1
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    algebraic equation

    I have an equation I need to solve. I have an answer but I don't have much confidence in it.

    here is the problem:

    "20 kg/m^3 = 1027 kg/m^3 + [.15 kg/m^3 (5 degrees C) + .78 kg/m^3(s-35)]. solve for s"

    the answer I got is 94.16. please tell me if I am off and also please advise on how you got there. Many thanks.
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  2. #2
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    Re: algebraic equation

    Quote Originally Posted by willowthewisp View Post
    I have an equation I need to solve. I have an answer but I don't have much confidence in it.

    here is the problem:

    "20 kg/m^3 = 1027 kg/m^3 + [.15 kg/m^3 (5 degrees C) + .78 kg/m^3(s-35)]. solve for s"

    the answer I got is 94.16. please tell me if I am off and also please advise on how you got there. Many thanks.
    I'd say you were way off since I substituted 94.16 for s in the right side of your equation and got nowhere close to the 20 on the left.

    I also question your use of units ... what happens to the units of Celsius temp? Maybe you should post the original problem in its entirety.
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  3. #3
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    Re: algebraic equation

    the original equation is - "density = 1027 kg/m^3 + [a (temp - 10 degrees C) + b (S-35)]" solve for S

    the constant (a) is .15 kg/m^3 and the constant (b) is .78 kg/m^3. based on a previous problem, I know density is 20 and the temperature is 15 degree C.

    I hope that clarifies things a bit.
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  4. #4
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    Re: algebraic equation

    No, that's not possible. If a has units of kg/m^3, a(temp- 10 degrees C) would have units of "kg(degrees C)/m^3" and cannot be added to "1027 kg/m^3".
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  5. #5
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    Re: algebraic equation

    Quote Originally Posted by willowthewisp View Post
    the original equation is - "density = 1027 kg/m^3 + [a (temp - 10 degrees C) + b (S-35)]" solve for S

    the constant (a) is .15 kg/m^3 and the constant (b) is .78 kg/m^3. based on a previous problem, I know density is 20 and the temperature is 15 degree C.

    I hope that clarifies things a bit.
    Then s \approx -1257 , for whatever units that variable represents ... a physical quantity/parameter ?

    I still take issue with the units ... how do units of density, \frac{kg}{m^3} \cdot (^\circ C) become \frac{kg}{m^3} ?
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  6. #6
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    Re: algebraic equation

    thanks. S is for water salinity. I'm not sure about the units either.
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