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Math Help - HELP WITH DOUBLING FUNCTION D(t)!!!!

  1. #1
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    HELP WITH DOUBLING FUNCTION D(t)!!!!

    I am stuck on this prolbem..if someone can explain it to me better or just guide me through it that would be great!..Thanks for your help!

    1. The doubling function D(t) 1n(2)/1n(1+r) gives the number of years required to double the amount of money invested at the interest rate r (expressed as a decimal), compounded annually. How long will it take to double your money at an interest rate of 3.25%?




    2. How long will it take to double your money at an interest rate of 5%?





    3. What interest rate would you need to double yoru money in 11 years?
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  2. #2
    Senior Member topher0805's Avatar
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    Your equation is a bit confusing... Is this what you meant?

    D(t) = \frac {ln 2}{ln (1+r)}
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  3. #3
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    Yes that is correct

    Sorry..I just got singed up with this website..and I don't know how to type in fractons like that
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  4. #4
    Senior Member topher0805's Avatar
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    Ok, this equation does not make any sense. D(t) implies that D is dependent on the variable t, but there is no t in the equation.

    Are you sure that you didn't meant this?:

    <br />
T(r) = \frac {ln 2}{ln (1+r)}<br />
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  5. #5
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    my bad..yes I did mean that.
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  6. #6
    Senior Member topher0805's Avatar
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    For the first two questions simply plug in 0.0325 and 0.05 for r to get your answers.

    For the third question, set it equal to 11 and solve for r:

    <br />
11=\frac {ln 2}{ln (1+r)}<br />

    Solve for r...
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