Results 1 to 8 of 8

Math Help - exponential growth

  1. #1
    Member
    Joined
    Nov 2005
    Posts
    172

    exponential growth

    If a bacteria culture starts with 8000 bateria and doubles every 25 minutes, how many minutes will it take the population to reach 43000?

    i need help setting up this problem, formula: y = Ce^(kt)
    so far i have 43000 = 8000e^(25)k
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    Nov 2005
    Posts
    172
    ok here what i gotten sofar:

    43000 = 8000e^(25t)

    (43/8) = e^(25t)

    ln(43/8) = 25t

    (ln(43/8)) / 25 = t

    so t = 0.67270 approx.
    not sure what im doing wrong but the answer is wrong
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Oct 2006
    Posts
    81
    you are in my calc II class too?

    No calcs=an adjustment. Kind of stupid to require that when it is obvious you need them for the homework.

    i think i finally realize i need to get a tutor. i do everything exactly like i think I should, but my answers are hit or miss. it's so frustrating not knowing the one error you are making.

    I don't know about this problem either. I thought I had it but my answers aren't working.

    BTW, I am doing it exactly like you.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    Nov 2005
    Posts
    172
    yeah.. this class sucks. she doesnt allow notes on the test, so im going to be screwed cuz i dont have a good memory.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Oct 2006
    Posts
    81
    Yeah, same. As bad as our last teacher taught in class at least he compensated for it on his tests. This teacher is fairly good, but she is a harder teacher. I always feel like I have this stuff down until webwork or a quiz comes, then I think I don't know it at all.
    Last edited by ThePerfectHacker; January 25th 2007 at 07:03 PM.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Global Moderator

    Joined
    Nov 2005
    From
    New York City
    Posts
    10,616
    Thanks
    9
    You guys in the same class?
    What chances are this of happening
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Member
    Joined
    Oct 2006
    Posts
    81
    Yep. We had the same teacher last semester as well as this semester. There is actually a third person in the same situation that comes here

    for future reference, the general formula to solve this is

    Pf=Po*e^(kt)

    k=ln(2)/(doublingtime)

    solve for t
    Last edited by thedoge; January 25th 2007 at 07:29 PM.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Super Member
    earboth's Avatar
    Joined
    Jan 2006
    From
    Germany
    Posts
    5,829
    Thanks
    123
    Quote Originally Posted by viet View Post
    If a bacteria culture starts with 8000 bateria and doubles every 25 minutes, how many minutes will it take the population to reach 43000?

    i need help setting up this problem, formula: y = Ce^(kt)
    so far i have 43000 = 8000e^(25)k
    Hello, Viet,

    according to your problem you have exactly 16000 bacteria after 25 minutes. Now you can calculate the constant k:

    16000=8000 \cdot e^{k \cdot 25} \Longleftrightarrow 25k=\ln\left(\frac{16000}{8000} \right) \Longleftrightarrow k \approx 0.027726. Solve for t:

    With these values you can solve the 2nd equation:

    43000=8000 \cdot e^{0.027726 \cdot t} \Longleftrightarrow 0.027726 \cdot t=\ln\left(\frac{43}{8} \right)

    t \approx 60.66 \text{ minutes}

    EB
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Exponential Growth
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: October 25th 2009, 09:52 PM
  2. exponential growth
    Posted in the Pre-Calculus Forum
    Replies: 0
    Last Post: November 6th 2008, 07:37 PM
  3. Exponential Growth
    Posted in the Calculus Forum
    Replies: 3
    Last Post: October 1st 2008, 08:17 AM
  4. Exponential Growth
    Posted in the Business Math Forum
    Replies: 1
    Last Post: September 10th 2008, 02:54 PM
  5. exponential growth help
    Posted in the Calculus Forum
    Replies: 1
    Last Post: July 15th 2007, 04:16 PM

Search Tags


/mathhelpforum @mathhelpforum