What % of interest do i need to double investment in 4 years?

Originally Posted by fixfax12

Im currently working on my homework, but Im struggling with this problem, i guess it is extremly simple, but i can find the answere, i read something about 72 rule, but is this method legit?

Correction:

In year 2000 the income was 1840000 in year 2009 the income was 1713173, the upcoming interest for the next 4 years is stabel, what is the intrest if the income in year 2000 is doubled by 2014?

=RATE(15,0,-1840000,3680000)
4.73%

Rule of 72 states that you can find the number of years required to double your money by dividing the rate into 72

=72/4.73
=15.222

Close enough to 15 years

I need to find how many % interest, it should grow from 1713173 to 3680000 in 4 years.

thanks

Originally Posted by fixfax12

I need to find how many % interest, it should grow from 1713173 to 3680000 in 4 years.

thanks

I thought you originally stated differently

Originally Posted by fixfax12

what is the intrest if the income in year 2000 is doubled by 2014?

In Excel

=RATE(4, 0, -1713173, 3680000)
21.063%

With paper and pencil a

PV = FV (1+i)^-N
FV (1+i)^-N = PV
(1+i)^-N = PV / FV
(1+i)^N = FV / PV
1+i = ( FV / PV ) ^ (1/N)
i = [ ( FV / PV ) ^ (1/N) ] - 1

i = [ ( 3,680,000 / 1,713,173 ) ^ (1/4) ] - 1
i = [ ( 2.148061 ) ^ (0.25) ] - 1
i = [ 1.210630607 ] - 1
i = 0.210630607
i = 21.063%