Posted by **Shreya** on Tuesday, October 16, 2012 at 10:05pm.

Exponential Functions

A=P(X)^t/n

A-final amount

P-initial amount

X-growth rate

t-time

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 -
**Reiny**, Tuesday, October 16, 2012 at 10:14pm
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 -
**Shreya**, Tuesday, October 16, 2012 at 10:18pm
Oh so they always have to be in hours? growth periods are always in hours?

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