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Math Help - Finding an unknown value

  1. #1
    Senior Member
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    Finding an unknown value

    Starting a new thread because I made a muck of the last attempt.

    1 divided by u, + 1 divided by v, = 1 divided by f

    I am required to find the value of V

    If u = 4/5

    If f = 2/3

    V = !

    4/5 - 2/3 = 2/15

    2/15 = 3 x 2 = 6 = 2
    ..........3 x 5 15 5

    so is my value V = 5?

    I am not sure and think there must be another way to ensure the numerator is equal to 1

    Thanks

    David
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  2. #2
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    Re: Finding an unknown value

    For this problem you need to solve the equation for v.

    Start by substituting the algebraic terms with the values provided, i.e. u = {4}{5} and f = {2}{3}.

    Therefore, the equation is as follows:

    {1}{4/5} + {1}{v} = {1}{2/3}

    This becomes:

    {5}{4} + {1}{v} = {3}{2} - because having '1' on top of a fraction inverts the fraction.

    The equation is then solved as follows:

    {5v}{4v} + {4}{4v} = {3}{2}
    {5v+4}{4v} = {3}{2}
    10v+8 = 12v
    8 = 2v
    v = 4
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  3. #3
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    Re: Finding an unknown value

    For this problem you need to solve the equation for v.

    Start by substituting the algebraic terms with the values provided, i.e.
    u = 4/5 and
    f = 2/3.

    Therefore, the equation is as follows:

    {1}/{4}/{5} + 1/v = 1/2/3

    This becomes:

    5/4 + 1/v = 3/2 - because having '1' on top of a fraction inverts the fraction.

    The equation is then solved as follows:

    5v/4v + 4/4v = 3/2
    {5v+4}/{4v} = 3/2
    10v+8 = 12v
    8 = 2v
    v = 4
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  4. #4
    MHF Contributor
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    Ottawa, Canada
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    Re: Finding an unknown value

    Quote Originally Posted by David Green View Post
    1 divided by u, + 1 divided by v, = 1 divided by f

    I am required to find the value of V

    If u = 4/5

    If f = 2/3
    Your work is very "messy", David.

    Equation is:
    1/u + 1/v = 1/f ; isolate v term on left:
    1/v = 1/f - 1/u ; substitute values:
    1/v = 1/(2/3) - 1/(4/5) ; simplify
    1/v = 3/2 - 5/4
    1/v = 6/4 - 5/4
    1/v = 1/4
    v = 4
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