1500 is invested at an annual interest rate of 9 compounded

$1500 is invested at an annual interest rate of 9% compounded annually. How long will it take for the investment to double?

Solution

\"compounded continuously\" then formula is ,
A = Pe^(rt)
if investment is \"doubled\" then A=2P:
plug in :
2P = Pe^(0.09t)
2 = e^(0.09t)
ln(2) =0.09t
ln(2)/0.09 = t
7.7 years = t

t = 7.7 years.