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Math Help - Please help me solve this problem

  1. #1
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    Question Please help me solve this problem

    Suppose y varies directly as x and y=27 when x=3. Find x when y = 45.

    I need help with one.
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  2. #2
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    Direct variation

    Suppose y varies directly as x and y=27 when x=3. Find x when y = 45.

    'Varies directly' most likely means an equation of the form y = x + k
    Where k is a constant. So as x increases by some amount, y increases by that same amount.

    change in y = change in x

    y2 - y1 = x2 - x1
    45 - 27 = x2 - 3
    18 = x2 - 3
    21 = x2

    when y = 45, x = 21
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  3. #3
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    Thank you so much I just forgot the formula then.
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  4. #4
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    Here is one way.

    "y varies directly as x"
    y ------> x
    y = kx ----the equation.

    y=27 when x=3
    27 = k*3
    k = 27/3 = 9

    When y = 45,
    45 = 9x
    x = 45/9 = 5 ---answer.

    ---------------------------------
    Another meaning of "y varies directly as x" is:
    if x goes higher, then y goes higher too; if x goes lower, then y goes lower too....proportionately.
    Last edited by ticbol; July 3rd 2005 at 12:45 PM.
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  5. #5
    Site Founder MathGuru's Avatar
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    Varies directly

    Ticbol's answer may be more correct than mine.


    It depends on what is meant by varies directly.
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  6. #6
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    thanks again
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