college algebra
posted by kate .
how long will it take an investment of $5000 to grow to $8000 if it is invested at 7.8% per year compounded weekly?

assuming 52 weeks per year
i = .078/52 = .0015
5000(1.0015)^n= 8000
1.0015^n = 1.6
log (1.0015^n) = log 1.6
nlog1.0015 = log 1.6
n = log1.6/log1.0015 = 316.57 monts
= 6.03 years
it would take 6 years 
Suppose that $5,000 is invested in an account at an annual interest rate of 5.1%
compounded continuously. How long (to the nearest tenth of a year) will it take for
the investment to double in size?