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Math Help - direct variation...

  1. #1
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    direct variation...

    not so good with word problems :/
    i know you use the direct variation formulas but sometime u have different situations where you add in other variables


    A company has found that the demand for its product varies inversely as the price of the product. When the price is 3.5 dollars, the demand is 500 units. Find a mathematical model that gives the demand in terms of the price in dollars.

    y= ___
    then approximate the demand when the price is 6.25 dollars.
    answer::


    & another one i have played around with:

    Let


    ??
    i know you have to replace the x's with Y's so that its

    x=y+2/y+10 and then a common factor but the rest i forget
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by bharriga View Post
    not so good with word problems :/
    i know you use the direct variation formulas but sometime u have different situations where you add in other variables


    A company has found that the demand for its product varies inversely as the price of the product. When the price is 3.5 dollars, the demand is 500 units. Find a mathematical model that gives the demand in terms of the price in dollars.

    y= ___
    then approximate the demand when the price is 6.25 dollars.
    answer::
    Inversely proportional means
    y = \frac{k}{x}
    where k is a constant.

    -Dan
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by bharriga View Post
    Let


    ??
    i know you have to replace the x's with Y's so that its

    x=y+2/y+10 and then a common factor but the rest i forget
    You do indeed have the correct approach.
    y = \frac{x + 2}{x + 10}

    Becomes:
    x = \frac{y + 2}{y + 10}

    x(y + 10) = y + 2

    xy + 10x = y + 2

    xy - y = 2 - 10x

    (x - 2)y = 2 - 10x

    y = \frac{2 - 10x}{x - 2}

    -Dan
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