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Exponential Functions


A-final amount
P-initial amount
X-growth rate
n-number of growth periods

The teacher had this question as an example and did it however i do not understand one thing:

The Ebola virus double every 30 min. If there are currently 2000 ebola viruses present in petrie dish, how many are present in 7 hours from now?

A=2000(2)^7/0.5 = 32768000

^ What I don't get about that is where he got the 0.5 from? Isnt it supposed to be 30 min? so 30? cause that's the growth period :|

  • Pre-Calculus -

    Your exponents should have been defined in hours

    so 30 minutes = 30/60 hours = 1/2 or 0.5 hours

    it says, the virus doubles every 30 minutes
    so how do you "double" something? Don't you multiply by 2 ?

    so the fixed part of the equation is
    A = 2000(2)^(t/.5)

    your only input is t, namely the number of hours you are dealing with
    suppose we look at 2 hours , so after
    30 minutes we have 4000 , after
    60 minutes we have 8000 , after
    90 minutes we have 16000, after
    120 minutes we have 32000

    and 2000(2)^(2/.5)
    = 2000(2^4)
    = 2000(16)
    = 32000

    I think n is poorly defined.
    I would have defined n as the doubling period expressed in hours.

  • Pre-Calculus -

    Oh so they always have to be in hours? growth periods are always in hours?

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