math
posted by anonymous on .
marcia has $220,000 saved for her retirement. How long will it take for the investment to double in value if it earns 6% interest compounded continuously?

See http://www.moneychimp.com/articles/finworks/continuous_compounding.htm
for the exact answer (11.56 yrs), or use the "rule of 72*" and get about 12 years.
*The product of the annual interest rate and the number of years must be 72 to double your money. 
i didn't get the right answer :[
the answer must be 139 months 
In your case,
440000=220000*e^0.06t
2=e^0.06t
ln2 = 0.06t
t= ln2/0.06
= 11.5524 years x 12 months
=139 months