Exponential Functions

[Becky4paws]

It is estimated that the population of a certain country grows exponentially. If the population was 60 million in 1986 and 90 million in 1991, what will the population be in 2001?

I have no idea how to even begin this problem - there is no example like this in my book. Can you get me started?

 

[skeeter]

use the law of natural exponential growth, P = P_oe^kt

let 1986 be t = 0 ... 1991 would be t = 5

P_o, the initial population is 60 million

P = 60e^kt

at t = 5 (1991), the population is 90 million ...

90 = 60e^k*5

3/2 = e^5k

ln(3/2) = 5k

k = ln(3/2)/5 = approx 0.081

using the value of k (also called the growth constant) ...

P = 60e^kt

2001 is t = 15 ... evaluate P for t = 15.