PreCalculus
posted by Shreya on .
Exponential Functions
A=P(X)^t/n
Afinal amount
Pinitial amount
Xgrowth rate
ttime
nnumber 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 :

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