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Thread: Salt Solutions

  1. #1
    Member harpazo's Avatar
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    Salt Solutions

    How much water must be evaporated from 32 ounces of a 4 percent salt solution to make 6 percent salt solution?

    Let w = water that must be evaporated

    w + 32(0.04) = 0.06(w + 32)

    Correct equation set up?
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  2. #2
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    Re: Salt Solutions

    I'm afraid you are very confused. 32 oz of a 4% solution will be 32(0.04) salt but it makes no sense to add w oz of water to 32(0.04) oz of salt!
    You can calculate that the solution originally contains 32(0.04)= 1.28 oz of salt. Evaporating x oz of water from0 that means that we have the same amount of salt but 32- x oz of water. The concentration is now 1.28/(32- x)= 0.06. Solve that for x.
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  3. #3
    Member harpazo's Avatar
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    Re: Salt Solutions

    1.28/(32- x)= 0.06

    1.28 = 0.06(32 - x)

    1.28 = 1.92 - 0.06x

    1.28 - 1.92 = -0.06x

    -0.64 = -0.06x

    -0.64/-0.06 = x

    10.6666666667 = x

    10.67 = x

    Correct?
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  4. #4
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    Re: Salt Solutions

    You can do that type using li'l diagram (w = water):

    32 @ 4
    -w @ 0
    -----------
    32-w @ 6

    4*32 / (32-w) = 6

    Solve: w = 32/3 (or ~10.67)
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  5. #5
    Member harpazo's Avatar
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    Re: Salt Solutions

    Quote Originally Posted by DenisB View Post
    You can do that type using li'l diagram (w = water):

    32 @ 4
    -w @ 0
    -----------
    32-w @ 6

    4*32 / (32-w) = 6

    Solve: w = 32/3 (or ~10.67)
    My biggest problem now and back in my student days is setting up the right equation leading to the answer. Lacking this skill has kept me away from tutoring jobs in my local area. Tutoring is a great way to make money. As long as I continue to struggle with word problems, tutoring for money is just a distant thought.
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    Re: Salt Solutions

    Quote Originally Posted by harpazo View Post
    How much water must be evaporated from 32 ounces of a 4 percent salt solution to make 6 percent salt solution?

    Let w = water that must be evaporated
    Quote Originally Posted by harpazo View Post
    .
    .
    .

    10.67 = x

    Correct?
    You were asked how much water. What are the units?

    They are ounces (actually fluid ounces, as opposed to weight).


    Your answer would be that there are about 10.67 ounces.

    Or, there are exactly $\displaystyle \ 10\tfrac{2}{3} \ $ ounces of water.
    Last edited by greg1313; Nov 7th 2018 at 01:52 PM.
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  7. #7
    Member harpazo's Avatar
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    Re: Salt Solutions

    Quote Originally Posted by greg1313 View Post
    You were asked how much water. What are the units?

    They are ounces (actually fluid ounces, as opposed to weight).


    Your answer would be that there are about 10.67 ounces.

    Or, there are exactly $\displaystyle \ 10\tfrac{2}{3} \ $ ounces of water.
    Yes, I forgot the units.
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