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Homework Help: Exponential growth and compound interest

  1. May 23, 2016 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    A = P(1+i)^n
    3. The attempt at a solution
    Here is my attempted solution, can someone please verify if my method is correct!
    Thanks in advance!

  2. jcsd
  3. May 23, 2016 #2

    Ray Vickson

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    Homework Helper

    It looks OK.
  4. May 23, 2016 #3


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    This is a good example of the "rule of 72", which is a rule of thumb used by financial people. Basically it says that the number of years it takes for an investment to double is equal to 72 divided by the annual percentage rate. In this case 72/4 = 18, quite close to your more exact solution.
  5. May 24, 2016 #4
    ok thanks for the help!
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