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Math Help - log question

  1. #1
    Super Member
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    Dec 2008
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    log question

    Hi
    I need help on the following question:

    If prices are increasing at the rate of 7.8% per year write down an equation for prices as a function of time. How long does it take for prices to double? How long does it take for prices to treble?

    I have found the equation:
    P = Po(1+\frac{7.8}{100})^t

    To find t i transpose the equation to get:
    \frac{log(P)-log(Po)}{log(1.078)}=t

    now i don't know how to find how long does it take for prices to double or treble, because what will the values be for P and Po?

    P.S
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  2. #2
    Super Member

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    Lexington, MA (USA)
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    Hello, Paymemoney!

    Your work is correct . . .

    \text{I would write it like this: }\;t \:=\:\frac{\log\left(\dfrac{P}{P_o}\right)}{\log(1  .078)}


    If the price doubles, then P will be twice the initial price P_o.

    . . Hence: . \frac{P}{P_o} \:=\:2


    Got it?

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  3. #3
    Super Member
    Joined
    Dec 2008
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    yep thanks i get it.
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