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Math Help - log question help

  1. #1
    Newbie
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    log question help

    so the equation is
    house price = A(2.7)^kt
    t= time in years
    A and k are constants
    price is 112486 when t=3
    price is 131593 when t=7

    question is to work out A and k

    I've been working on it for atleast an hour and i'm stumped
    help would be greately appreciated
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  2. #2
    Junior Member shinhidora's Avatar
    Joined
    Jun 2008
    Posts
    56
    Quote Originally Posted by immunofort View Post
    so the equation is
    house price = A(2.7)^kt
    t= time in years
    A and k are constants
    price is 112486 when t=3
    price is 131593 when t=7

    question is to work out A and k

    I've been working on it for atleast an hour and i'm stumped
    help would be greately appreciated
    No idea how you do it Anyway this is what I tried xD

    Note: THIS IS WRONG! so don't read it if you get easily confused

    1st Try

    112486 = a (2.7)^3k
    112486 = 3ak log 2.7
    112486 / 3k log 2.7 = a

    Replace a in your original equation

    112486 = (112468 / 3k log 2.7) 2.7^3k
    112486 = (112468 / 3k log 2.7) 3k log 2.7
    112486 = 112486

    So obviously replacing a was the wrong thing to do, so let's try replacing k.

    2nd Try

    112486 = a (2.7)^3k
    112486 = 3ak log 2.7
    112486 / 3a log 2.7 = k

    Replace k in your original equation

    112486 = a (2.7)^3(112486 / 3a log 2.7)
    112486 = a 3(112486 / 3a log 2.7) log (2.7)
    112486 = 3a log 2.7 (112486 / 3a log 2.7)
    112486 = (3a log 2.7 112486) / ((3a log 2.7)^2)
    112486 = 112486 / 3a log 2.7
    112486^2 = 3a log 2.7
    112486^2 / 3log 2.7 = a

    Now let's find k

    112486 / 3a log 2.7 = k
    112486 / (3 (112486^2 / 3 log 2.7) log 2.7) = k
    112486 / (3 (112486^2 /3) = k
    112486 / 112486 = k
    1 = k

    Now let's see if it works out... So replace everything in your original equation.

    112486 = a (2.7)^3k
    112486 = (112486^2 / 3log 2.7) (2.7) ^ 3*1
    112486 = 19.683 (112486^2 / 3log 2.7)
    112486 = 19.683 * 1819362976
    = Wrong xD

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  3. #3
    Newbie
    Joined
    Jan 2008
    Posts
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    image

    I'm thinking maybe i missed out something when i described the problem, I have uploaded a image of the text


    oh and even better if you can help me out with question 5
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