looking for help with continuously compounded interest... how do you find initial investment and annual percent rate given the time to double is 7 yrs and amount after 10 yrs is 2400?

Question

adamaero · Answer

Some more good info: http://www.harpercollege.edu/mhealy/ecogif/uein/rule70.gif

paxpolaris · Answer

$$\Large A=P e ^{rt}$$

anonymous · Answer

i know the formula but I'm not sure how to find it

paxpolaris · Answer

doubles in 7 years :$$\Large 2P = Pe^{r \cdot 7}$$

solve for r

anonymous · Answer

so r=9.9%?

paxpolaris · Answer

right

anonymous · Answer

thx so much!

anonymous · Answer

how do i find the initial?

paxpolaris · Answer

amount after 10 years is 2400

just plug in:
A=2400
t=10
r= 0.09902

and solve for P

anonymous · Answer

i divided 2400 by e^9.9 and it gave me a decimal

paxpolaris · Answer

e^0.99

anonymous · Answer

thanks again

anonymous · Answer

Determine the time necessary for P dollars to double when it is invested at interest rate r compounded monthly, daily. r =3.4%

anonymous · Answer

sorry I'm so lost;/

adamaero · Answer

http://www.harpercollege.edu/mhealy/ecogif/uein/rule70.gif

adamaero · Answer

except you have to do extra since it's not a year but $$\frac{ 1 }{ 12 }th$$
of a year and $$\frac{ 1 }{ 52 }$$ of a year.