# Math Help - Solving for interest rate

1. ## Solving for interest rate

At what rate of interest does it take six years of compounding monthly for an account to double in value?

How do you get from,
(1+r/12)^72=2 to

r= 12(2^(1/72)-1)

2. i really don't get what you needed.. but if you are just solving for $r$ in $\left({\frac{1+r}{12}}\right)^{72} = 2$, then that is just simple algebra(and i think, there was a mistake in your grouping..)..

first, get the 72nd root of both sides, you will have $\frac{1+r}{12} = 2^{\frac{1}{72}}$

then multiply 12 to both sides, $1+r = (12)(2^{\frac{1}{72}})$

lastly, subtract 1 to both sides, $r = (12)(2^{\frac{1}{72}}) - 1$

now, is that what you want?

3. ## Yes

Thank you very much