If interest is compounded continuosly, after t
years the amount in the account is A=Pe^rt
(where A =total amount, P=origanal amount invested, and r=interest rate).
How long does it take for your investment
to double at 4% interest? round to the nearest
year9 if your original amount is x, the doubled
amount is...

Question

If interest is compounded continuosly, after t 
years the amount in the account is A=Pe^rt
(where A =total amount, P=origanal amount invested, and r=interest rate).  
How long does it take for your investment
to double at 4% interest? round to the nearest
year9 if your original amount is x, the doubled
amount is...

anonymous · Answer

A = 2P , r = 0.04 , t =? 
2P = Pe^rt 
2 = e^0.04t
ln2=0.04t lne 
t= ln2/0.04 
t = 17.32