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Math Help - Solving for interest rate

  1. #1
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    Solving for interest rate

    At what rate of interest does it take six years of compounding monthly for an account to double in value?

    How do you get from,
    (1+r/12)^72=2 to

    r= 12(2^(1/72)-1)
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  2. #2
    MHF Contributor kalagota's Avatar
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    Taguig City, Philippines
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    i really don't get what you needed.. but if you are just solving for r in \left({\frac{1+r}{12}}\right)^{72} = 2, then that is just simple algebra(and i think, there was a mistake in your grouping..)..

    first, get the 72nd root of both sides, you will have \frac{1+r}{12} = 2^{\frac{1}{72}}

    then multiply 12 to both sides, 1+r = (12)(2^{\frac{1}{72}})

    lastly, subtract 1 to both sides, r = (12)(2^{\frac{1}{72}}) - 1

    now, is that what you want?
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  3. #3
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    Yes

    Thank you very much
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