MathExponential Functions
posted by Kate .
Suppose an investment of $500 doubles in value every 15 years. How much is the investment worth after 30 years? After 45 years?
please help!!! i don't even understand how to approach this problem! =(

Initial investment = $500
Investment value after 15 years
= $500*2
= $1000 (doubles)
15 more years later (30), value of investment
= $1000 * 2
= $2000 (doubles from 15 years ago)
I will leave it to you to calculate the value of investment at 45 years from the initial investment.
Mathematically, let P = initial principal,
2P = PR^15 (R=interest rate)
R=e^(ln(2)/15)=1.047294123
Value of investment after N years,
V(N)=$500*R^N
for N=15,
V(15)=$500*1.047294123^15
=$1000.00
V(30)=$500*1.047294123^30
=$2000.00
and so on. 
after 30 yrs the investment is worth $2,000
after 45 yrs the investment is worth $4,000