SOLUTION: If you invest $300 at 2.25% compounded monthly, how many years (to the nearest hundredth) would it take to grow your investment to $1,200?

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: If you invest $300 at 2.25% compounded monthly, how many years (to the nearest hundredth) would it take to grow your investment to $1,200?      Log On


   

Question 1192939: If you invest $300 at 2.25% compounded monthly, how many years (to the nearest hundredth) would it take to grow your investment to $1,200?
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
P=Po(1+I/t)^nt
1200=300(1+.0225/12)^12t
4=1.001874^12t
ln both sides
ln4=12t ln 1.001874
round at end
t=ln 4/ln 1.001874
=61.67 years
-
rough check with rule of 72 for doubling time: 72/2.25=32 years.
The money has to double twice, so estimate 64 years, a decent estimate. If you use 69.3/2.25, which is much more accurate, the time for two doublings is 61.60 years.