posted by Bill .
If $8,500 is invested at 6% compounded continuously, how long will it take to double the investment?
future value = present value * ert
where t=number of periods, and r=rate
future value/present value = 2
take natural log on both sides,
0.06t = ln(2)
The rule of 69
In fact, you can apply the rule of 69 for continuous compounding:
the time (in years) to double is 69.31 divided by the annual rate in %.