Question

Do anyone know the annual rate and time to double equation for an investment

Answer 1

72/rate

Answer 2

you need one or the other. rate or time. what exactly is the question?
oh right, rule of 72 is a good approximation.

Answer 3

\[Number of years 2 double = \frac{72}{Interest Rate} years\]

Answer 4

Initial Investment $600
Amount after 10 years 19,205.00
What is the annual % rate?
What is the time to double?

Answer 5

here rate is equal to 41.425 %

Answer 6

and time to double is 1.73 years

Answer 7

just solve 2=(1+rate)^x

Answer 8

solve
\[600(1+r)^{10}=19,205\] for r
\[(1+r)^{10}=\frac{3841}{120}=32\](rounded)
\[1+r=\sqrt[10]{32}=\sqrt{2}\]

Answer 9

that is a hell of a rate of interest

Answer 10

\[r=\sqrt{2}-1=.4142\] as sheg said. but rounded it is
\[.412421\] not
\[.412425\]

Answer 11

time to double solve
\[1.41421^x=2\]
\[x=\frac{\ln(2)}{\ln(1.4121)}\]

Answer 12

I think sheg's interest rate assumes continuous compound interest and satellites is compounded yearly.
don't understand sheg's doubling time. It should be very close to 2 years.

Answer 13

@PHI
dear friend in case of compound interest u earn interest on principal as well as interest earned

formula for compounding is

\[Amount = Principal \times (1 + r )^n\]

now do this problem
Principal,P = $ 1000
rate, r = 41.425 %
Number of years, n = 2 years
and see how much amount u have after 2 years

Answer 14

http://www.wolframalpha.com/input/?i=1.41425%5E2

Answer 15

http://www.moneychimp.com/features/rule72.htm

Answer 16

actually if u will make aproximation then it will double in 1.73 yrs because i was using the rule of 72