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Homework Help: Size of a bacteria colony

  1. Sep 3, 2006 #1
    We're on the section of logarithms, so I'm guessing this has something to do with them...

    If the size of a bacteria colony doubles in 5 hours, how long will it take for the number of bacteria to triple?

    I know that doubling time and all that stuff is independent of the amount of something you have...

    Should I use P = P0at or P = P0ekt ?

    I'll just try it both ways to show some work, but I don't know which equation i'd be using...

    first with P = P0at
    2 = 1a5
    2 = a5
    a = 21/5
    a = 1.1487

    3 = (1.1487)t
    ln3 = tln(1.1487)
    t = ln3 / ln1.1487
    t = 7.92473 hours

    Now, to try using P = P0ekt

    2 = 1e5k
    2 = e5k
    ln2 = 5k
    k = ln2 / 5
    k = .138629

    3 = 1e.138629t
    3 = e.138629t
    ln3 = .138629t
    t = ln3 / .138629
    t = 7.92484 hours

    very close answers, which one equation should i have used, and is the answer right?
  2. jcsd
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