Results 1 to 5 of 5

Math Help - Solving for rate (removal of logs)

  1. #1
    Newbie
    Joined
    Dec 2010
    Posts
    2

    Solving for rate (removal of logs)

    Hi

    I am trying to solve for r in the following:

    F=P(1+r)^t

    I've got it to: log(t) =log(F/P) / Log(1+r)

    can someone please show me the step by step stages to make r the subject? How do i remove the logs?

    Many thanks

    H
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,549
    Thanks
    1418
    No need for logarithms...

    \displaystyle F=P(1+r)^t

    \displaystyle \frac{F}{P} = (1+r)^t

    \displaystyle \left(\frac{F}{P}\right)^{\frac{1}{t}} = \left[(1+r)^t\right]^{\frac{1}{t}}

    \displaystyle \left(\frac{F}{P}\right)^{\frac{1}{t}} = 1 + r

    \displaystyle \left(\frac{F}{P}\right)^{\frac{1}{t}} - 1 = r.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Dec 2010
    Posts
    2
    thanks a million for this!

    follow up question - how would i solve the equation if i used logs from the stage i mentioned....would it be possible without going through a 10 stage process?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,549
    Thanks
    1418
    You only use logarithms if you are solving for the exponent.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,693
    Thanks
    1466
    Quote Originally Posted by hisab View Post
    Hi

    I am trying to solve for r in the following:

    F=P(1+r)^t

    I've got it to: log(t) =log(F/P) / Log(1+r)
    This is wrong. log(a^b)= b log(a), not "log(b)log(a)". From
    F/P= (1+ r)^t, taking the logarithm of both sides give log(F/P)= t(log(1+ r)) so that log(1+ r)= (1/t) log(F/P)= log((F/P)^{1/t}). Now take the "anti-log" (exponential) of both sides to get 1+ r= (F/P)^{1/t} and so r= (F/P)^{1/t}- 1, exactly what Prove It said.

    can someone please show me the step by step stages to make r the subject? How do i remove the logs?

    Many thanks

    H
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Solving for x with logs
    Posted in the Pre-Calculus Forum
    Replies: 7
    Last Post: July 23rd 2010, 12:41 AM
  2. Solving with logs
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: November 10th 2009, 09:49 PM
  3. Solving Logs
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: September 19th 2009, 03:42 PM
  4. Replies: 10
    Last Post: July 15th 2009, 07:17 PM
  5. Logs solving for x
    Posted in the Algebra Forum
    Replies: 1
    Last Post: March 23rd 2009, 04:11 PM

Search Tags


/mathhelpforum @mathhelpforum