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At what rate of interest?

  1. Jan 8, 2015 #1
    1. The problem statement, all variables and given/known data
    At what rate of interest, compounded continuously, will a bank deposit double in value in 8 years?

    2. Relevant equations
    None.

    3. The attempt at a solution
    Q0e8r=2Q0
    e8r=2
    8r=ln(2)
    r=ln(2)/8
    But the answer is (25/2)ln(2)%. How do I get the answer from there?
     
  2. jcsd
  3. Jan 8, 2015 #2

    Ray Vickson

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    Science Advisor
    Homework Helper

    Be careful about units.
     
  4. Jan 8, 2015 #3
    Thank you for reminding me about units. I got it! Thanks a lot!
     
  5. Jan 8, 2015 #4
    MY father pointed out that doubling of principal occurs - approx 72 / Rate ...... while not accurate enough for an answer, a quick check of you are in the ball park... 9 vs 8.66
     
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