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Math Help - Setting up an Equation and solving....

  1. #1
    Newbie
    Joined
    Oct 2007
    Posts
    4

    Setting up an Equation and solving....

    I need to reverse a formula that was given to me in an equation.

    The problem is..
    For the following function, C computes the cost in millions of dollars of implementing a city recycling project when x percent of the citizens participate.

    The formula is

    C(x) = 1.5x
    100 - x

    I solved that...... now it says...

    Using this model, estimate the percentage of participation that can be excepted if $5 million is spent on this recycling project? Set up an equation and solve algebraically. Round to the nearest whole percent.

    I have no clue how to turn the equation around.

    It's been 25 years since I took algebra in highschool and I'm expected to regurgitate it for College Algebra... can anyone atleast help me with setting up the formula?

    Thanks in advance!!
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  2. #2
    MHF Contributor
    Joined
    Apr 2005
    Posts
    1,631
    If
    C(x) = 1.5x / (100 -x)
    then
    what is x when C(x) = 5?

    That is what the problem ask you.

    5 = 1.5x / (100 -x)
    Clear the fraction, multiply both sides by (100 -x),
    5(100 -x) = 1.5x

    500 -5x = 1.5x
    500 = 1.5x +5x
    500 = 6.5x
    x = 500/6.5 = 76.923 percent

    That is 77 percent of the population participating. ---answer.
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  3. #3
    Newbie
    Joined
    Oct 2007
    Posts
    4

    Thumbs up

    OMG....

    I would never have guessed to do that...

    Thanks so much!!!
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