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Math Help - how should i solve this question?

  1. #1
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    Question how should i solve this question?

    The copper content of an alloy is 60%. If 1 kg of copper is added into the alloy, the copper content of the alloy will increase to 70%.
    a. Find the original weight of the alloy.
    b. Find the percentage change in the weight of the alloy.

    I am learning about percentage change and found this question in my textbook. I don't know how to solve this question. Could you please help me? Thank you.
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  2. #2
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    Re: how should i solve this question?

    if n1 kg of a% alloy is mixed with n2 kg of b% alloy
    then resultant alloy will have C%=(a*n1+b*n2)/(n1+n2)% alloy of n1+n2 kg.

    let n kg of 60% alloy is taken
    and 1 kg of 100%(pure copper) is taken
    if mixed, we get C= 70% alloy.
    i think you can do it now
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  3. #3
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    Re: how should i solve this question?

    Thanks for your information, but i don't really get it. I think for many days, still don't know how to finish the question. Can you show me how to set up the first step of the question?
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  4. #4
    Member Veronica1999's Avatar
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    Re: how should i solve this question?

    Lets say the alloy is X kg.
    Then the copper content is 0.6 X kg.
    If one kg of copper is added to the alloy the the copper content is now 0.6X + 1.

    The copper content should now be 70% of X+1.

    0.6X + 1 / X + 1 = 0.7

    Once you sove for X you will be able to find the percent change by calculating 1/X times 100
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  5. #5
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    Re: how should i solve this question?

    Thank you very much. I got it now.
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  6. #6
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    Re: how should i solve this question?

    Quote Originally Posted by Veronica1999 View Post
    0.6X + 1 / X + 1 = 0.7
    There is no real solution to that, Veronica;
    also no solution to 0.6X + 1 / (X + 1) = 0.7

    Hamsters: you got what?!
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  7. #7
    Member Veronica1999's Avatar
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    Re: how should i solve this question?

    Wilmer,
    Are you not familiar with basic algebra?

    0.6X + 1 = 0.7X + 0.7

    0.1X = 0.3

    x= 3

    Therefore copper 1.8

    2.8/4 = 70%
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  8. #8
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    Re: how should i solve this question?

    Quote Originally Posted by Veronica1999 View Post
    Wilmer,
    Are you not familiar with basic algebra?
    0.6X + 1 = 0.7X + 0.7
    0.1X = 0.3
    x= 3
    Therefore copper 1.8
    2.8/4 = 70%
    AGREE, but ONLY if equation is: (0.6X + 1) / (X + 1) = 0.7

    Your posted equation was: 0.6X + 1 / X + 1 = 0.7

    Are you not familiar with basic order of operations?

    Also not a good idea (confusing to student) to switch from X to x within same solution.
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  9. #9
    Member Veronica1999's Avatar
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    Re: how should i solve this question?

    But if you understand the context of the problem
    that kind of misunderstanding is less likely to happen....
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  10. #10
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    Re: how should i solve this question?

    There was NO misunderstanding on my part.
    I did not attempt to solve the original problem.
    I simply tried to solve YOUR equation, which has no real solution.

    For you to call omission of brackets a misunderstanding....well, no comments.
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